[1.1.91] Constant desync issues on vanilla MP game

[TeflonMike]

I've posted this issue under bugs already but i did some deeper investigation and decided to make a new post here.

I'm actually at my wits end here and i'm begging for help.
So every time i join an MP server the game desyncs, regardless if it's a public server or closed one with friends. Game is 100% vanilla mind you, no mods.

Things i have done to find a solution:
- reinstalled the game
- deleted the crop-cache.dat and temp folders
- disabled steam cloud
- tried running factorio as admin
- opened ports on my router and in windows firewall
- tried playing from a bootable linux usb
- reinstalled windows
- tried connecting though a separate internet connection (cellular tethering via USB)
- tried disabling the XMP profile

All of this to no avail. What else can i do to be able to play Factorio with friends again, right now this game is beyond broken for me and i'm out of ideas what to troubleshoot next. I can provide heaps of desync logs if anyone is interested in looking into them and helping me out with this. Also this is the only game i have any issues in, all other (usually more hardware demanding) games are fine in both single- and multiplayer.

PC Specs:
CPU: AMD Ryzen 7 5800X
CPU Cooler: Corsair iCUE H100i RGB PRO XT AIO
Motherboard: Gigabyte B550 AORUS Elite V2
RAM: 2x16GB Kingston HyperX DDR4 3600
GPU: Gigabyte GeForce RTX 3070 GAMING OC
SSD 0: Crucial P2 1TB NVMe M.2
SSD 1: Crucial MX500
Storage: Seagate 1TB & Western Digital Black 2TB
PSU: Corsair RM750x

[Loewchen]

Any crashes or bluescreens?

[TeflonMike]

no, just desyncs on factorio. Rest of the PC is fine (at least it seems like it, never had any other issues)

[Rseding91]

Does it desync instantly? If yes, can you reproduce the desync on a new 50x50 limited size map and post the desync report here?

[TeflonMike]

50x50 didn't desync (tried running it through localhost), my standard savegames (again, localhost, running on the same machine) do tho. I don't know if it's any help. Same with public vanilla servers I've never joined before, instant desync or within a minute.

[TeflonMike]

https://drive.google.com/file/d/1Cl4VwK ... sp=sharing

here's the first desync on a brand new default, vanilla map. it's not 50x50 but it seems reproduceable (just takes time since it seems to be dependant on save game complexity)

[Rseding91]

The differences in that desync are around fluid in pipes and steam engines running differently compared to the people you're playing with. Something so common that likely everyone playing multiplayer would be desyncing if there was a game bug around it.

Can you test something - it will take a while. Start a new game with the replay feature enabled and play until you research a decent number of red and green sciences normally. Using cheats or what ever is fine - just as long as there's some actual builds running with steam engines and such.

After doing that for a while save the game and try to watch the replay to the end.

I'm wondering if it will fail to watch the replay on your own system. I also wonder if the replay will work for other people.

At this point I'm thinking that your CPU is executing code incorrectly and it's resulting in different floating point values when doing electric and fluid simulation logic. Because if it's not that; I have zero other ideas. Even if it is that - I don't have a fix for it.