If you allow players to morph into r15 animation packages in-game (superhero, bubbly, vampire etc) you might also be experiencing this issue.
We started having this problem a couple of months ago (around when rthro was released) players would sit really low in seats:
Turns out it was only when a player was using an in-game animation package: we were grabbing animation IDs out of a script in ServerStorage, and it appears that roblox changed their “sit” animation from rbxassetid://507768133 to rbxassetid://2506281703 somewhere maybe around October-ish
Here it is fixed!
A lot of the r15 animation packages you get from the toolbox still have the old sit ID and will cause this issue.
This was one of the issues that came out around this time, and maybe this is why they changed their sit animation: (dated November 6th 2018)
That problem there seemed to fix by itself. However the sit animation ID fix honestly took us way too long to start to deeply investigate on our end because there were a lot of animation problems that happened around this time as well. Anyone else have all of their animations break around late October? (by break I mean arms completely popping out of their sockets). We fixed THAT issue by creating all new animations off my own rig instead of using ROBLOX’s woman rig you spawn out of the animation editor (the one we used previously).
Inevitably, scaling has caused all sorts of problems with animations… it sucks to have to remake every single one. I already messaged roblox about this problem but I am just wondering if anyone else experienced this… I don’t see people mention this and other games SEEM fine so it’s a bit confusing 
now we are getting onto another topic
I’ll probably make a different topic about this but here’s the picture example of what happened to our animations:
How it appears in editor
What it actually did in game, ever since release of rthro
