Mobs with crossbows do not have an arrow, although they can still shoot. Bug occurs on the latest version of lithium on Modrinth.

Lithium only: https://user-images.githubusercontent.com/47220489/194306270-85420a1b-6a85-48c4-ba9d-15450285af7a.mp4
Pure vanilla: https://user-images.githubusercontent.com/47220489/194306476-17c5521d-13ed-4ee9-ae3d-4ce2f9326ea5.mp4

Related to a previous issue about foxes still showing the item after they ate it

mixin.entity.skip_equipment_change_check=false fixes this bug