Currently I'm in the middle of the third expansion of this set. Never had any complaints, untill I was prepping for the most recent session. I use my laptop and tablet together, mainly using the compendium on the tablet and my laptop purely for extra info and the maps. 
However, upon trying to open the sourcebook on the tablet, I noticed I couldnt access it. It basically said I dont have the sourcebooks. I couldnt open any of the 4 books, instead being redirected to the marketplace. I tried reinstalling, logging out and logging back in, nothing really worked. I tried it in my phone, and I had the same issue there. It also seems to only be with these specific books. 
On the laptop I also encountered some bugs. I can still access the books on pc (which makes clear that I do indeed have the licence), but there are some creatures I cant access like before. Normally I could click any creature I saw in my sourcebook and get redirected to the creature page, because it's included in said sourcebook. Now however, these creatures are suddenly locked behind tons of other books I dont have, and thus I get directed to the marketplace again. This is becoming very annoying.
I would love some help with this.

Edit to add: like mentioned, currently busy in the 3rd part of this adventure, Sleeping Dragon's Wake. There's a dragon at the Bronze Shrine, which I cant access. When I hover above it, it says 'This content is part of the Sleeping Dragon's Wake digital content pack. Click to visit the Marketplace for purchasing options'. I am in Sleeping Dragon's Wake. When I go to said marketplace, it also says I have it previously purchased, as do I have the seperate sources in the sourcebook, as I have the entire book. When I click the source I want (the dragon), I just get back to the same marketplace page again.
I got the books with the code from the essentials kit. 

On the web interface, click on you user avatar in the upper right. Choose account. Click on the marketplace tab. Look for the Account entitlements section. Do you need to sync?  If so, click the button. (If all is well, there will be no button)  

if that doesn’t do it, make sure you are signed in to the right account. It’s actually fairly common for folks to inadvertently have two accounts 

The first thing worked for me! Thank you! I have no idea how that happened tho, since I didnt have the problem for months of use. It just suddenly appeared. I guess it randomly desynced or something?

I dont have two accounts, so that definitely wasnt the issue. 

Thank you though for your help, I can finally see everything properly again ^^

A few months ago they started moving from all the the DDB data being in one monolithic service to a batch of interrelated micro-services.  That requires syncing entitlements, and sometimes they get out of sync.  I don't think it's anything we do on our end.  I usually have to verify that I remember the pathway to the spot to check entitlements correctly when I respond to posts like yours, and a couple of times my own entitlements have been out of sync when I've done so, which has surprised me; but it's easy enough to fix, once a person knows to check there.