this was a 4 mod crash along with Berry good, Autumnity, and Buzzier Bees
https://pastebin.com/H3zJwT6H

What's "FastUtil"? That's the common denominator here.

Maybe JEI? Did a quick search and it linked to the JEI mod

It is mentioned in the above link

mezz/JustEnoughItems@576fb94

The crash appears to be on Autumnity.

It is true Autumnity is part to blame, however Quark and all the other errored mods in that log are equally culpable. The log shows all these mods using non thread safe code from inappropriately placed registration during the common setup event. Since common setup is dispatched in parallel, you can only correctly run code which supports concurrency. It so happens that ComposterBlock#registerCompostable does not, nor dispenser behavior registrations, flammability info, and a number of other map data structures. The relevant registry events are when these actions should be taken instead, as these events are synchronous or if required DeferredWorkQueue.

for records purposes here's their Autumnity report Markus1002/Autumnity/issues/11