[2.0.69] Adding, Updating, Deleting Mods causes a desync or Migration issue

[Zacosham]

So, me and the spouse have a world that we've spent months working on. We've found ourselves in a bit of a weird spot, we have a handful of mods installed... which the game runs fine. However, if I add anymore mods, take away any mods, or update any of our existing mods we immediately get desync's the moment both of us are in the game. Usually what triggers the desync is everything is fine for 8 to 10 seconds but if one of us checks the map, it causes it to immediately happen.

The frustrating part, is if I roll every mod back to exactly the original our game/save becomes playable again. I dont know where to even start trying to figure this out. I tried understanding a few desync guides, but since we are able to play as long as we change nothing I didn't know if I should try posting in the desync with mod area or not.

Would really love some help, just not sure what to do next.

What did you do?
Any changes to our mods at all add/sub/delete then play together

What Happened?
Within 8 to 10 seconds we crash one the 2nd player joins the server

What did you expect to happen?
We've been able to play 100s of hours without issue as long as we do not change our mods. The second we do anything, we start desync'ing until we revert all the mods

Does it always happen?
We can reproduce it over and over once the 2nd player hits the game


Thanks,
Log File:

World Save:
https://drive.google.com/file/d/1U7eT1T ... drive_link

Desync Just Incase It's Helpful:
https://drive.google.com/file/d/1J69VkU ... drive_link

[Loewchen]

Sounds like there is a migration triggered by changing mods that is causing this.

[Zacosham]

Is there anyway to upload what I have and have someone help me check, or explain to me what I can try to do and I'll work to see if I can figure it out?

[Loewchen]

See 52433.

[Zacosham]

Thanks again Loewchen, I think all the requested is attached now. Sorry for the issues before

[Zacosham]

Google drive link fixed, thanks for the heads up!

[Loewchen]

A dev would have to look into this and that might take a while. If you can continue playing with the old mod loadout I'd suggest doing that instead of waiting for a fix.

[Zacosham]

Another plot twist, the latest patch when it downloaded also broke our game so we are now 100% unable to play together on our 1000+ hour save. Is there something I can try to debug this myself?

Thanks,
Z

[Rseding91]

It’s possible the underlying desync is an engine bug, but desyncs are *the* hardest thing to diagnose and fix.

Essentially the only somewhat reliable way is a 100% reproduction on our end. That requires the save file and exact steps to reproduce the desync that works every time they’re performed.

It sounds like that might be possible in your case?

[Gorfiend7]

I did some testing with the provided save, and was also getting desyncs shortly after joining. Then I tried re-saving it and loading that, and did not desync after several minutes looking around.

I've also been having similar desync issues in a game with my friends, and it seems like the same conditions. We have a lot of the same mods, so it's looking likely the issue is one of them doesn't handle migrations in a multi-player safe way.

@zacosham, can you try loading the save with different mods, re-saving it, then loading that, and see if you still get the desync?

So if that's the case, now it's just a matter of finding out which mod is breaking it... is there any good way to do that other than turning mods off until it works?

[robot256]

I was bored so I did a code review on all the mods in your save file. TWO mods stand out as ones which write to potentially dangerous session-global variables inside on_configuration_changed: "Long Range Delivery Drones" and "Corrundum". Removing one or both of them, loading it in single player, and re-saving may cause the desync to go away when you copy it back to the server.

[Zacosham]

Oh my goodness, you two are my heros, I was able to upgrade all the mods, then boot into single player, resave and reload once more and presto the desync 100% stopped. THANK YOU ALL SO MUCH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!