I encountered desync recently. I read the docs about the "global"variable again. The metatable feature of lua might cause this. I removed all the metatable in my code just now. But I found it in gvv.
I'm curious whether the desync is gone if all the metatables are gone.
I'll keep working on this. No idea if I can eventually find the solution.

https://forums.factorio.com/viewtopic.php?f=25&t=97983

Any idea?

Still I can't catch any clue of what can cause desync while using metatable in my code...
There are possibility of desync when seeing structure of target mod depending on how target mod written. Reason why is that gvv GUI & "global" elements are broadcasted along clients and syncronisity is reviewed by server and client. So a desync can be caused when gvv touches "almost forgotten and non-wellwritten" part of target mod.
Or, loading ability of "_G" of gvv mod also can cause desync if target mod is not designed _G part to be synced. Reason why is that gvv pulls submerged "_G" part of target mod to revealed surface and forces it to be checked syncronisity via GUI and own global table of gvv.

Hello,
The variables in "_G" must never change state because they change in the player who is going to use your mod but not in the others. This is what causes desynchronization.
Variables in "_G" are either constants or functions that will be called. (So it's not really variables I know)
Thank you.