Mob movement and sync issues?

[MTM123]

Description

I'm adding trying to add spiders that can jump on you:
https://gist.github.com/MTM123/68bb4cce00db6e2a73308050fdbe449a
basically the idea of the code is that they mount you as soon as they are close to your head (see tick())
The problem is that as soon as they mount you they are stuck in the air and doesn't really move with the player or they just are stuck on the ground for some reason.

An issue I also have and it might be related is that the block are getting blown up and entities are discarded:
https://streamable.com/7bt1tu
but they don't really die even and there seems to be issue with client and server seeing different things it seems (destroyed blocks)

[MTM123]

I guess I should provide version of minecraft and fabric as well