The crash happened after I connected a mechanical pump to Electrolyzer from Advanced Rocketry to pull liquid oxygen into another machine. It didn't happen immediately, I was able to play the game just fine for about 5 minutes and then suddenly crash.

I cannot re-join that world again after the crash.

Crash Report

crash-2021-04-21_21.44.37-server.txt

The source of this issue appears to be a fluid typing problem which occurs with other mods (like Mekanism), not just Create. Advanced Rocketry has reported this issue here: Advanced-Rocketry/AdvancedRocketry#2070

If you really need the fluid, you can actually get it via creative mode, or by pumping the fluid into the spout with a hand crank, and then coming back to your world after the game has crashed and you restart your minecraft files. It'll only get you a bucket per crash.

You can rejoin the world by simply disabling advanced rocketry. You won't need to disable libvulpes, so you'll be able to keep your ores and some of your blocks.

In my modpack, Immersive Engineering's pipe was able to safely transfer this fluid without a crash so I think there's at least some way to work around this issue.

I will leave the issue open for now but if the dev doesn't feel like supporting this edge case, feel free to close it.

The issue got fixed upstream. Closing this now.