Minecraft version: 1.20.1
Modloader: Forge
Forge version: 47.2.30
Environment: Singleplayer and Multiplayer

First mod name: Grabby Mobs
First mod version: 1.5

Second mod name: Eidolon: Repraised
Second mod version: 0.3.8.9

There is a step in the Eidolon mod where you have to throw the mod's guidebook (Ars Ecclesia) to a witch who is then supposed to drop the book with additional mod info written into the book (from my understanding, experienced by a friend). With both these mods installed together, when the book is dropped it is instantaneously picked back up and will not give the book back to the player, resulting in the mod not progressing further. I could resolve this myself but unfortunately I couldn't find an entity blacklist config option if Grabby Mobs has one.