"Invalid Player Data"

Me and my friend created a modded server with one mod (Identity Mod, Fabric) everything was going well

Until I used the /kill command on myself to return to spawn. When I died, I couldn't hit respawn (When I clicked it, it just greyed out and came back again). The only thing I could do I was leave. If I tried to rejoin, an error occurred, saying "Invalid Player Data". When I looked at the log, some random things appeared along with the words "Unsafety Timed Out, Unsafety Left the Game." The only thing i could do was delete my player file, which fixed the error temporarily but reset all the mobs I had on the mod. As well as everything I had.

Some time later, my friend died to a skeleton. And the same thing happened. And now it wont stop happening.

My friend suggested using quick respawn, which I tried. When I died and the error occurred, I was glitched in place with the camera shaking. I could still place blocks, but that was it. Leaving the server led to the "Invalid Player Data" error.

Can someone explain why this is happening? I am not cracked, and my friend isnt either. Its extremely annoying and I dont want to give up on the world.

I did. But the error happens again if I die a few more times after resetting.