Describe the Bug

It's on Minecraft 1.20.1 FABRIC

I have around 10 train contraptions circling around an area around 32+ chunks.
It's on a hosted server.
The game run at an average of 80 fps. But the fps drops down to 0/20 for 20/30 secs then returns to normal.
This happens everywhere in this 32 chunks area, around all 5/10 minutes (it's reccurent but random).
It's the same lag I have when I log on the server and the game is loading the chunks.
I tried to optimize it with better chunk loading, which works fine, like the log lag have almost disapeard, but this is issue is still there.
I also tried using entity distance. I tried with the minimal and the maximal render distance (up to 512 blocks). The bug was still there in both configurations. So it's not a render issue I'd say.. and the fps were still good overhaul.

As it is now, it looks to me like a chunk loading/unloading issue with the contraption (this bug doesn't happens in area without contraptions).

I have put together all the optimisation mods I could find but yet nothing have yet seems to do a real difference for this issue.
I tried to optimise the cpu render thread, did nothing, the same for the ram, I went from 28gb to 8gb hoping it was a kind of memory issue (too uch ram isn't good) but it did nothing.
Also the server is on OMG-Server, I can't modify the ram nor the Java argument. The server is supposed to dynamically gives enough ram to the game.

I have many mods, but everything else than this area is running just fine.

Reproduction Steps

1. have many trains contraptions circling in a 32 chunks area
2. wait for some minutes
3. experience huge lags for up to 30 secs
   ...

Expected Result

The game not lagging randomly

Screenshots and Videos

No response

Crash Report or Log

No response

Operating System

Windows 11

Mod Version

0.5.1f

Minecraft Version

1.20.1

Other Mods

No response

Additional Context

No response