We've been playing fine for over a month but now it seems that we've run into an error, while my brother is hosting the server, I can't join anymore.
When the game is paused, I can join but the moment it unpauses, it also runs into a desync.
Since my pc can't be on full-time it's also not really an option for me to host it.

Would it be possible to see what in the modpack is causing the issue? I can't seem to figure it out on my own.
Desync report: https://www.dropbox.com/s/6du1l8laeo1hbd5/desync-report-2024-01-31_18-00-29.zip?dl=0

After disabling most mods that we're not going to be using in this modpack desyncs have become slightly less common but still happen.
Here is my latest desync report: https://www.dropbox.com/s/5h5jl0lwgczzrwu/desync-report-2024-02-01_06-20-17.zip?dl=0

Okay, so it seems we were able to pinpoint the issue.
It seems to have been the [url=https://mods.factorio.com/mod/belt-balancer-performance]belt balancer mod[/url], especially the part in this screenshot: https://forums.factorio.com/download/file.php?id=80817.
When they are not too loaded, and are only handling a single resource, everything seems to be fine (after disabling the mod we seem to have 940 of them in our factories), but when handling high-load multi resource belts, it seems to fail.