Instead of trying to find the problem, I would suggest you all obtain copies of the mods from a single source. For example, send your friends copies of your mods through discord or email or whatever. They can back up their version of the mods and then re-install the mods using the files you sent.
If that doesn't work, the next thing I would try is:
Use those mods (that you got from a single source) but all players disable all of their UI mods, you play and see if there's a desync. It seems unlikely that a UI mod would interact with sim mods in a way that would cause desyncs, but ya never know. Computers are complicated, in theory it could happen. So I would try that next.
