Hello,
I have been running my own 1.20.1 Forge server for at least a year now, updating the modpack and adding mods along the way as my playerbase grew. Recently, I have had an issue where when the server is online for a while (used to be 8 hours, now it is 3), it starts to lag heavily, to the point of being borderline unplayable.

I cannot figure out what it is using Spark profiler because Spark crashes instantly on my server. When I checked the debug file, I noticed that it was spamming something about "FabricRegistrySync" trying to start "registry saves" and "not saving empty registry data". I do not have Sinytra Connector installed so I have no idea what could be causing this. I hope someone can figure it out.

https://mclo.gs/e1JVml1 - debug. Again, no spark because it crashes on my server.

Add the crash-report generated with using spark

I managed to get spark loader working by changing ModernFix configs, and I found that one issue was with Cataclysm projectile entities not despawning. I will leave the server on for some more hours and if it starts lagging again, I will provide a new debug log and spark profiler log.