Several times now we've had a popup show when we tried to join the server (after loading the map):

"Notice
Cannot join. The following mod event handlers are not identical between you and the server. This indicates that the following mods are not multiplayer (save/load) safe. (see the log file for more details):

mod-train-scaling"

This is the log file:

98.049 Error ClientMultiplayerManager.cpp:1113: mod-train-scaling was registered for the following nth_ticks when the map was saved but has not re-registered them as a result of loading: 5
98.049 Error ClientMultiplayerManager.cpp:96: MultiplayerManager failed: "" + multiplayer.script-event-mismatch + "
" + "

I think we have to restart the server to fix it but I can't try it right now. I think we disabled and enabled the mod last time this happened. This time the server is empty but last time it had one client on it while the other one could not join.
This is on factorio 0.17.31, train scaling 0.17.3.

That's really strange - I can't wrap my head around how the tick handler would still be attached with the queue empty. I'll do some digging on my end, but I might need to release a new version with some more logging when this happens to figure it out... Can you tell what causes this to start happening? Seems like it would start triggering after either a train's built successfully, after a train build's aborted, or after a train's deconstructed.