[0.15.5] Many users desyncing (contains heavy mode data)

[I_IBlackI_I]

On our FactorioMMO world we got a lot of user desyncing again, I was not there but we did manage to get the heavy-mode data and a folder for our users to upload their desync-reports.

https://blackstonei.stackstorage.com/s/w4uezDJOCSXKU97

If this is again related to the global.player_spectator_character there may be an bug regarding indexing.

[posila]

Thank you very much for the heavy-mode results. There is definitely some save/load instability with heat-pipes and that causes desyncs.

[posila]

Should be fixed for 0.15.6.
Thanks again for all the data.

[I_IBlackI_I]

May I know what the actual cause was of this desync?

[posila]

It is silly, almost embarrassing.
When you place an entity with heat-buffer, it searches for adjacent entities with heat-buffers in order to connect to them. These connections are not saved and are recreated on load. But on load every entity searches for neighbors to connect to, and when creating a connection it didn't check if the connection already existed. So every heat pipe connection was duplicated and as a result heat transfer was twice as fast.
It is such a stupid bug it blows my mind we didn't caught it during playtesting.

[Vegemeister]

Is this related to the build-order-sensitivity of heat pipes?