The Crucible is somewhat broken. On my 1.16.4 Minecraft Server, the Crucible crashes every time one of the steps of a recipe is performed (for example throwing in a mushroom for the sprouting fungus recipe). Logging in afterwards reveals that the recipe did progress (in this case, the water turned purple), but I think this is still a pretty big issue.

In case you're wondering, it does work fine on singleplayer, it only crashes the server.

Could you please post the crash report?

I've managed to reproduce this locally, I think there's a pretty simple cause. Should be fixed in the next commit.

Should be fixed in 89b517b.