When using a refined storage grid:

when just viewing player inventory:

Minecraft:1.16.3
JEI Version: jei-1.16.3-7.6.0.51
Forge:34.1.42

I don't know why it's happening but please god make it stop. Probably a clash with ftb chunks/quests gui buttons?

Thanks for the report!
Fixed in the latest version.

can confirm. pack im using is ftb unstable 1.16. Happens on all gui scales, each with increasing size.
happens for me with a status effect, but it'll even happen in a furnace gui or any other gui.