Hey folks,  The Cataclysm Bolt is broken.  It adds to the "to hit" of the hand crossbow.  

Just tested and nope, it does not.

Either you're mistaken or using a homebrew version.

I'm not sure how you tested, but I've been able to recreate it across my own account with no homebrew as well as two of my players. 

The item is here:

https://www.dndbeyond.com/magic-items/7170916-cataclysm-bolts

I made my character public and you can see how activating/disactivating the magic item adjusts the "to hit":

https://www.dndbeyond.com/characters/110315795/MGRMC8

You're using a homebrew version. 

Click the item, in the sidebar at top it says "Version:"  this means it is homebrew. Remove item. Get the real one. Add that. Your problem will be resolved.

See the difference:

Your version (homebrew)

My version (the official item)

In my homebrew items there are no items with that name or anything like that name.

I shared the link above.  If you click it, you'll see the reference: "Tal’Dorei Campaign Setting Reborn, pg. 194"

So update:  

Looks like the item was shared with me from another campaign I'm in.  Dang I wish the listing was better at showing homebrew vs. original content.

Thanks for the tip on "version"!  That's helpful!  Can confirm the published version is correct.