The cause is unclear, but desynchronization occurs with a high probability immediately upon server connection. While trying repeatedly may sometimes result in a successful connection, it is very inconvenient. My server is also running the CargoShip mod, and there were no issues when using CargoShip.

I am very curious as to why this mod causes multiplayer desynchronization. I really enjoy this mod, so I sincerely hope the issue can be resolved.

Thank you.

I made a mistake and forgot to mention, the issue occurs when operating the locomotive.

Interesting! I haven't actually tested this in multiplayer now that I think about it, which is kind of a glaring oversight on my part. Regardless, the mod isn't actually clientside as you may expect; it's all ran on the server (including volume settings, unfortunately.)

I won't be able to tonight, but I'll see if I can't hammer out a patch/workaround tomorrow in the small window I have before heading to work. Admittedly, I'm very much so a novice to Factorio modding, so my plan (at the moment) is to basically just stop the script from running whenever a player is joining and pray that works.

Released a potential fix. A few major variables, improperly, were local variables instead of ones in Storage. This meant that, unless those variables were perfectly synchronized on load by chance, you'd desync.

I'm short on time so I can't test in multiplayer, but it does still work in singleplayer (including from existing saves and also new saves), so please let me know if the fix worked ^^