Just was flying around in nether when it crashed. "server closed" and brought me to multiplayer. It looked like the world got deleted as it wouldn't let me enter back into the world, really strange. I tried a bunch of times to get it to boot, updated quark and Zeta, and it worked! For a little bit, went onto the nether roof and was running around up there when the same crash happened.

https://mclo.gs/PW9MxTb

Here is the log. Thanks. Says the issue is quark. I doubt its an incompatibility since the game has been running fine for weeks.