Minecraft Version

1.21.x

Forge Version

21.1.72

Vampirism Version

1.10.0

Incompatible mod

Lithium mc1.21.1-0.14.0-BETA.1

Singleplayer/Multiplayer

Both

What happened?

when you transform into a bat, you can't fly

Reproduce steps

1. You enter the world of single player or multiplayer
2. You transform into a vampire (at night in the overworld)
3. When you press double space, you don't fly

Understand that the lithium mod is in beta and can be fixed in the future.

I report it mainly if this information helps someone

Relevant log output

No response

As a solution to use vampirism and lithium to fly with bat mode. In the Lithium.properties configuration you can add the following line:

mixin.collections.attributes=false

At least it worked for me
It only fails on the client (no modification needs to be made on the server)