While riding mounts, leaving and rejoining server makes the mount disappear entirely in servers.

[beltxd]

Describe the bug
For example, iceandfire hippogryphs are flying mounts. When riding them in middair and disconnecting from the server and rejoining, the hippogryphs disappear. This occurs with other mounts as well from different mods, such as the moa Aether Legacy. I tried to disable certain settings in the config that may seem related to my issue such as

        # Makes the motion checker even more aggressive.
        B:aggressiveMotionChecker=false

        # Aggressively checks for invalid living entity movement and attempts to fix it
        B:"Motion Checker"=false

        # Synchronizes dismounts with players more aggressively
        B:"Player Dismount Sync"=false

however, disabling these options did not help at all.

Reproducibility
Please try to reproduce the issue with as few other mods as possible. Then check one of the following checkboxes according to your results. To check a checkbox replace the space between the square brackets with an x (like this [x]) or create the issue and check the checkbox by clicking on it.

• [x ] I reproduced this issue with as few other mods as possible installed.
• I am unable to reproduce this issue consistently.

To Reproduce
I only included RLTweaker, Ice and fire and aether (examples for mounted mobs) and hosted it from either side from client and server sided.

Versions
RLTweaker: 0.7.5
Forge: 2860
Minecraft:
Other mods (necessary to reproduce the bug): iceandfire and aether (possibly any mod that includes mounts).

Log File
https://mclo.gs/9H5vSpd server log.