The window of Factorio (on Windows) has a slight issue that it shows a 1 or 2 pixel border around the window. When it's maximized, it's easily noticeable compared to other applications that run maximized.

Following what I read on reddit , I've tried it myself as well.
Basically, Factorio has the ...

I only have the current save (autosaves because server, I don't save manually) and not the save from when the first desync + crash happened. Is that enough too?

And even if I desynced multiple times (even with 3 people at the same time after my previous post), I still don't know what exactly causes ...

Ah, I thought that the log file was enough since I got that message after the desync:
Unexpected error occurred. You can help us to solve the problem by posting the contents of the log file on the Factorio forums.

I looked for the right desync report, but apparently the game didn't create one. If ...

I was happily attaching red wires to some power poles and a combinator, and moving my mouse back and forth from and to my toolbar, when suddenly I got a desync from the server while holding the red wire in my hand and hovering over the toolbar.

Sadly, I can't seem to reproduce it at the moment. But ...

The desync also happens when holding a train stop.

Edit: didn't see it was already reported, sorry.