When a player connects, my MSPT goes up from 4 to 15-20 and runs the server.

Minecraft: 1.19 Fabric

I had such a problem on Forge, but I fixed it with some kind of mod, like FastLoad or krypton or ksyxis, but then I put a lot of optimization and I don't know how to fix it. When a player connects to the server, it freezes.

Can u just try with it just on client, and tell me if the issue persists. Test it by itself please!

ksyxis isnt supposed to be with fastload... and MSPT going up when a player joins is normal.

It's not normal, the server freezes when loading the player. On Forge, some mod fixed it, like APTweaks.

I don't use Fast Load and Ksuxis mods together.

I checked, the problem persists.

Did u try with just fastload?

yes, i use.

Is fastload both present on server and client?

yes

I tested it without your mod too.

Okay, can you join the discord for better means of communication?

ok

I actually do not know what is happening here, nor do I know how to reproduce/resolve this.

Ok, I figured it out. It is simply the product of the way this mod is made. This mod takes certain shortcuts that really shouldn't be done. There is no practical way to fix this.