We have confirmed that this mod causes this problem, it goes like this:
Download the newest version of FCB, opening the creative menu then clicking the [>] icon at the top, to change page, the game meets in unfortunate fate and crashes.
I'm bringing this to your attention as soon as I found out, so I'm hoping you can have a fix out for it just as fast.
Regards,
-L0ST

I cannot reproduce this, please provide crash log.

I can't find the log. I'll try get it later.

Okay!

Indeed I do, I could have sworn I fixed that for all of my mods, but I guess I forgot one. A new version of UnderwaterUtilities will be out shortly.

@L0ST5ILVER
I assume it is similar to this crash log.

@shadowfacts

https://github.com/shadowfacts/UnderwaterUtilities/blob/04396f411990433b3c0f3fb462e2062f70fb9fc9/src/main/kotlin/net/shadowfacts/underwaterutilities/block/tank/ItemBlockTank.kt#L30

Believe you need to add a method here,

for example: ChiselsAndBits/Chisels-and-Bits@fb38943#diff-617810317411c8f3ddf74d4e39088abb

This method seems to have changed in 1.12 for some reason or another.

I'll mark this as closed, unless @L0ST5ILVER has a second mod with the same problem. But I'll need a log to check on if that is the case.