Mass dropping items out of the player inventory via holding ctrl q and hovering, makes a large quantitiy of them diappear.
36 stacks dropped result in about 12 remaining, with the rest vanishing.

Minecraft Version 1.19.2

Mods installed:
Quilted Fabric API
Cloth Config API
Mod Menu
Mouse Tweaks

The issue does not exist, when mass dropping items, with item scrollers or inventory control tweaks drop matching items.
(tested on separate profiles)

nvm it's a vanilla bug, didn't expect that.