Hello! I'm getting a server overloaded error on my server that I've identified Quark to be the cause of (did the ol' trial and error, removing Quark fixes it).
Using latest version, 4.0-462. Forge 47.4.0.

To reproduce, I find the easiest way for testing purposes is to delete the world file and force it to regenerate so that the server is forced to generate chunks, as that usually triggers the overloaded error. Otherwise, having a player join the server will also do it.

In my own testing I've noticed that the behaviour primarily affects mobs, and they will lag around instead of moving smoothly, but this is pretty typical of high TPS. The lag is noticeable & error will appear regardless of what's going on if a player is in the server, but generating chunks & having entities on screen makes it worse.

latest (5).log

same question

"Can't keep up! Is the server overloaded?" is a standard Minecraft warning, and it's pretty common to see during worldgen in modded environments. It's not fatal and can usually be ignored unless it keeps happening during gameplay. Nothing here necessarily indicates Quark is at fault. How much RAM do you have allocated to the server? Can you get a Spark report?

It was continuous and caused a lot of lag. Unfortunately, I no longer have the same server setup as this was quite a while ago.
Ended up spending hours doing trial and error removing some mods that didn't play nice with Quark and other things, along with pre-generating the world with Chunky and that helped.