I literally don't have any save files in the game and I'm still using the Mobile Web version.... not a downloaded version.
As for downloaded saves, I only have 3 ... all less than 5Mb. 🤷♂️
I tried it today and it's fine for now... not sure what it was but it made bug testing my world very annoying lol.
Edit: It appears I have accident found the root cause, it's the xenomorph world in the shared worlds. Downloading it causes the worlds to get Thanos snapped when you exit world editing or the world you're playing in. I would assume it also causes the character bug though I'm not sure due to that world's lack of model. 🤷♂️