I'm getting this error today, which I did not get yesterday:

  90.251 Error ClientMultiplayerManager.cpp:1102: mod-mapshot was not registered for any events when the map was saved but has registered the following events as a result of loading: on_tick (ID 0)
  90.252 Error ClientMultiplayerManager.cpp:98: MultiplayerManager failed: "" + multiplayer.script-event-mismatch + "
" + "
mod-mapshot"
  90.252 Info ClientMultiplayerManager.cpp:589: UpdateTick(14613726) changing state from(ConnectedLoadingMap) to(Failed)
  97.324 Info ClientMultiplayerManager.cpp:210: Quitting multiplayer connection.
  97.324 Info ClientMultiplayerManager.cpp:589: UpdateTick(14613726) changing state from(Failed) to(Disconnected)
  97.599 Info UDPSocket.cpp:218: Closing socket
  97.599 Info UDPSocket.cpp:248: Socket closed
  98.862 Quitting: user-quit.
  99.731 Goodbye

I'm not particularly familiar with multiplayer, but I know that Factorio usually is fairly careful about mod consistency, which seems to be related. Also, mapshot uses on_tick only to detect something on startup and then unregister itself - I wonder if that related.

How did you get this error - do you load the mapshot mod in game or are you getting that from the CLI?

This was loading a mod part way through a playthrough, then saving the server and then restarting the server. It was after the server had re-started the game that users could no longer join.