Describe the bug

When mounting a flyable mount, such as a Hippogryph or tamed Amphithere, and touching water, the mount becomes invisible, the player without them but starts sinking into the ground as if they were still on the mount. Relogging/saving and leaving the world after to try and see if that helped, saw me AND the mount flung so high in the air that Aether Music was playing./The player and mount fail to render, causing an invisibility bug until you're teleported back down to the overworld or are able to fly long enough (Took me 5 minuets) to get down.

To Reproduce

1. Tame an Amphithere or Hippogryph.
2. Enter the water and attempt to take off.
3. Mount goes invisible, you begin sinking into the ground.
4. Relog, suddenly you're...
5. ... Yeah.
   

Expected behavior

Leaving the water/mount hopping out of the water to begin flying and not being flung into the Aether.

Modpack Version:
-3.0 BETA 5

Server or Singleplayer:

• Server

Version the world was created on:

• 3.0 BETA 5

Additional Context

I discovered this by accidentally in the water when trying to reposition my Amp onto a new landing pad for easy take off/landing. This was done on a server, with other people online.

From #820 (adjacent issue):

Clipping into blocks with your face while riding a hippogryph sometimes causes you to ghost dismount. This makes it look like you have been dismounted as you are no longer visually on the mount. However, the game still considers you mounted as pressing the dismount key will drop you next to the hippogryph. This is extremely terrifying, especially in the aether.

To reproduce, spawn in a hippogryph, ride it into a ceiling a few times (like a floating island or a cave ceiling)

I expect to be able to hit blocks with my face, take suffocation damage normally while remaining seated on my mount, both visually and technically.

sinking into the ground usually means that the chunk wasn't loaded - you relogging probably reloaded the chunk, the game realized you were in a block, and it sent you incredibly high up

Sounds about right, this would be a problem, but I was in my home base when I mounted...

So the chunk was loaded already. So unless mounting unloads the chunk you're in, I'm not sure what went awry.

From my experience of riding those mounts, they get buggy when interacting with the water or bumping a block above your head. For some reason, it dismounts you somehow, but the game still thinks you are on the mount so you are still flying. ( Something to do with sync issues) If it happens, press shift right away. you will return to your mount dismounted. The water thing can make your mount bounce.(Very annoying) The Amphithere is VERY buggy. I do not recommend it as a mount..