Nice idea.  Troublesome implementation.

The surprise implementation of this feature has thrown my inventory into disarray. 

All custom values deleted from containers.  If i had contents written in "notes" of an item, they're gone, now.  This is very bad. 
   no way to write new notes.     (custom "Notes" in many non-container items seem to still be there.  But deleted from many others.)
All custom weight values deleted from all items.  All the items that were in my Bag of Holding.  All Homebrew or house rule weights.  
All custom names reset from anything tagged "container".  Not only do I need to re-organize, but I have no idea what I've lost.

It's visually a mess.  I have a bunch of empty sacks and pouches.  Not to mention Flasks & vials.  It's a huge mess of stuff to scroll through.  At the top, and bottom of the Inventory pane.  That window was already very small.  thus requiring a lot of scrolling.  Now, with the space taken-up at the top, it's even smaller.

addendum:
Starting Equipment seems to have been reset.  Items seem to still be in inventory.
"containers cannot go into containers." - I can't put pouches into my bag of holding or backpack?   I suppose i understand why this is done for the system's sake, but it doesnt make sense in-game.

I have no way of knowing how much custom field info i have lost.  thus, how many items or details lost.  
I might be able to figure it out for 1 character.  but this is across multiple characters.  

No way to roll this back; to see a saved version?  a .pdf?

----

-you'll be able to specify what currency is in what container, but not place a pouch of coins into your backpack?
-empty containers are now just visual clutter.
-if you split your Equipment inventory into specific containers, that might be useful for organizing, for you, the player; but doesnt mesh with what's going on with your character.  not necessarily, at least. 
-it means it's mostly only good if you want to have your Equipment split into multiple, collapsible lists.  if you want to micro-manage what's in each bag; but still be able to see all your items in 1 list, for easy perusal; that will not be possible?

All Silvered & Adamantine info deleted from weapons!!!!

My custom item notes appear intact.

My biggest gripe is you can't add custom items to any container. Oh cool, I can separate my component pouch! Oh no, can't put anything in it.

All custom names reset.  not just from things tagged "container".  ALL!

This has completely screwed my character.  I had a ton of stuff recorded this way.
It is NOT OKAY for the system to just come-in and make changes to a person's sheet, without their foreknowledge or permission!  This is not acceptable.

and .pdf backups do not record/display all of those custom values.  even if i did have one for each character.
  (.pdf's only display 30 items of your inventory, even if you had 90.  And no custom notes are displayed.  I only have one backup; from 6 months ago.)

Please revert this immediately.  And re-implement this system once players (customers) have the option to select how it changes their sheets.

To-Hit Bonus and other custom fields, also reset.

Additionally: Portable Holes (and I'm assuming Bags of Holding) don't remove the weight from the character.

I had special enchantments, properties, descriptions of items recorded in the custom names, notes, etc.  And now all of that is erased.  
If you had container contents written in "Notes" of that container; they are now erased.
   (I'm just trying to emphasize why this is so bad; using an example that most can appreciate.)

Yeah, I lost all item customizations as well. And it's definitely a bug that you can't put custom items into a container. Also noticed you can't homebrew a container that will be recognized as such and allow you to put things in it. I agree there are some hiccups here but once those are ironed out I think it'll be a great addition. 

They've said that they're aware of the issue with customizations being missing and are working to try and restore them.

https://imgur.com/ibM0cFX

This is a problem

I did not lose any customizations of names, notes, or other settings for items...at least that I noticed. 

It wasn't everyone and it looks like they've recovered everything since.

As I said in another thread. Customization was erased/rolled back to customization from 6 months or more ago. Currency has been rolled back to several weeks or more ago. This is across more than one character too.

Roll-back absolutely everything to 48 hours ago (just before the new container system was launched).
Put it through more extensive testing. Make absolutely certain there will be no unintended interactions.

Then make these new, "functional" containers a separate item. So that they will not replace the existing ones, their names & notes.

Yes, there will be two versions of "Sack". One tagged to have this functionality, and one that is not. So what? At least that way, people will still be able to put 10 empty sacks in their inventory, and it'll just be a number.  Otherwise, make it an "archived" item; similar to rejected UA. Existing ones will remain, untouched; but you will no longer be able to put that "non-functional" version in your inventory. (You'll need to make it in homebrew). I worry that this still might erase the custom info fields. And it seems safer to just make two versions of each container.

Not sure if anyone else is having this issue, but my +to spell attack on my items isn’t registering. I should be +15 and it’s only showing +10.

It seems as though, perhaps, the deleted / rolled-back custom info has been restored.  Difficult to be certain if everything is fixed.

Custom notes have been re-introduced to functional containers. That's good.  (They don't display, next to the item, as most do.  You need to click into the Customize menu to read them.  That's less good.)

I eventually saw that Pocketmouse said it had been fixed hours before; but it was all still missing on my sheet. It required using a different device / browser / or a new tab (which seems odd). (There seems to be a long-running issue with the way the servers save and refresh data.  a separate matter.)
(Pictures in Homebrew items & monsters are displaying as broken links, at the moment.)  edit: (all uploaded pictures.  Including Character portraits.)

Situations like this can damage customer confidence, immensely.
I'm holding my breath, with a level of anxiety.  But if the developers do/did fix this unfortunate incident, in it's entirety; then I thank them for their diligent work.

Quote from funnelcakr >>

Yeah, I lost all item customizations as well. And it's definitely a bug that you can't put custom items into a container. Also noticed you can't homebrew a container that will be recognized as such and allow you to put things in it. I agree there are some hiccups here but once those are ironed out I think it'll be a great addition. 

Well, I had intended to disagree with you greatly, and to write a pretty harsh rant about this new container system. But after seeing that they've already rolled back some of the issues and have added customization, I've mellowed out a bit.

While I still dislike this system as it currently is--it could have been done MUCH simpler, but then again, this is the same team that thought the best way to do digital dice was by LITERALLY MODELING THE PHYSICS, trapping themselves into a box where they allegedly can't even speed up the rolls--I'm at least hopeful now that over time it'll become something we can use and benefit from without too much clutter/hassle/trouble/etc. Not sure if they planned on this being the final state, or if they just released it early so we'd have something; but either way, they seem to understand now that this still needs more work.

I'll just go over the things I hope they eventually correct:

- All containers in your inventory are now a completely separate separate section on your sheet, and no longer show up in your actual inventory. You HAVE to deal with them. If they'd just let you designate your own containers ("Hey, why does the Sack item have a "add a Sack container" button in the description?") they could be inventory line-items of their own, and the contents could just be (collapsible) listings indented beneath them.

- You cannot rename, re-weight or otherwise modify or customize these containers. Not even notes. Ok, they actually fixed this.

- You cannot create custom items that are containers. Again, if containers were just separate inventory line-items, this should be straightforward.

- You cannot add custom items to containers. I'm guessing this was just an oversight, because I don't see any logical reason for them to be excluded.

- You cannot put containers inside containers (seriously?) There are other ways to address the concerns that prompted this. Limit the number of nestings allowed. Only allow items to be moved "Out to Inventory," into a container in inventory (if they're also in inventory,) or into a container within the container they're in. Create a way to "explode" a container so all inner items, no matter how deeply nested, are just added to your inventory. Go with the suggestion to make "Sack items" and "Sack containers" separate things, and just disallow the container items, so you can at least put a "Sack" of some sort into your Bag of Holding.

 EDIT: - Removing a container removes all its contents. There should be two buttons for this, not one. One removes the container and all its contents. The other removes the container and moves all its contents to wherever the container was, either inventory or inside another container.

Quote from SteelTheory >>

It seems as though, perhaps, the deleted / rolled-back custom info has been restored.  Difficult to be certain if everything is fixed.

Custom notes have been re-introduced to functional containers. That's good.  (They don't display, next to the item, as most do.  You need to click into the Customize menu to read them.  That's less good.)

I eventually saw that Pocketmouse said it had been fixed hours before; but it was all still missing on my sheet. It required using a different device / browser / or a new tab (which seems odd). (There seems to be a long-running issue with the way the servers save and refresh data.  a separate matter.)
(Pictures in Homebrew items & monsters are displaying as broken links, at the moment.)

Situations like this can damage customer confidence, immensely.
I'm holding my breath, with a level of anxiety.  But if the developers do/did fix this unfortunate incident, in it's entirety; then I thank them for their diligent work.

 The customization has, the gold hasn't.

Quote from Porphy >>

Not sure if anyone else is having this issue, but my +to spell attack on my items isn’t registering. I should be +15 and it’s only showing +10.

 I’ve seen other reports that magic items in containers don’t apply their modifiers.