https://pastebin.com/Mxa7DRjJ

Currently running a 1.16.1 server with Quark-r2.3-266. We've had it crash randomly several times and this is the latest crash log to be produced. I've submitted it to the support team of our host who suggest it could be a Quark issue.

We currently run Biomes O Plenty, NetherPortalFix, Simple Farming, Guard Villagers, Comforts, Sit, and RE:Skin on the server as well. We're unable to update to the 1.16.3 version due to the changes in code to biomes which badly effect BOP.

Is there any way there could be a fix in the 1.16.1 version to sort this or is this not a Quark issue?

I don't believe this is a quark issue.

The most likely reason your support team suggested it is, is because there's a pointer to the quark ServerWorld mixin in the stack trace, but it's not changing any of the functions involved here.