When you move a drawer that has at least some contents in it, and you move it by repositioning it with your hands using the Carry On mod, the next time you left click it to get one item out, that slot would be permanently cleared from the drawer's contents.

I know the Carry On mod isn't necessarily supported, but it could still be that there is something wrong here that could be fixed.

How to reproduce:

1. Place any drawer (1x1, 1x2, 2x2)
2. Put in a stack of an item such as wheat seeds
3. Use both drawer keys on the drawer to lock and show amounts
4. Clear both hands and move the drawer to another blockspace
5. Left click the wheat seeds
   ❌ notice the entire stack is reduced to zero, but only one seed is in your hand

Version:
Minecraft: 1.16.4
Storage Drawers: 8.2.1
Carry On: 1.15.1.7
Forge: 35.1.13

We're seeing the same. It does appear to only affect on slot. In a single drawer its the only slot of course. In a 1x2 its the top slot, and in a 2x2 its the top left. Contents in the other slots do not seem to be impacted. Correction It doesn't matter which slot you click. The first slot you click after moving it loses anything above what you took out (1 or 64) After this the drawers functions normally again.

Single click out 1 item and you lose all the rest. Shift click a stack and you get a stack, but lose all the rest.

EDIT This occurs if the drawer is interacted with when locked. It seems that if you unlock the drawer first, then interact with a slot you do not lose anything and can the safely lock the drawer the drawer again. Haven't tried with an unlocked drawer.