I couldn't think of a better way to formalize this message. Here is a fragment of the log file:

95.391 Error ClientMultiplayerManager.cpp:1072: mod-Automatic_Train_Painter was not registered for the following events when the map was saved but has registered them as a result of loading: Custom event (ID 299), Custom event (ID 302) и Custom event (ID 303)
95.391 Error ClientMultiplayerManager.cpp:99: MultiplayerManager failed: "" + multiplayer.script-event-mismatch + "
" + "

There is an assumption who is doing this while using this mod with LTN

I get the msg: "A mod is not multiplayer (save/load) safe: Automatic Train Painter"

I've been using it in my games for a long time. Both single and multiplayer. I began to receive a similar error (which I wrote above) not long ago

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-Automatic_Train_Painter
Unfortunately I don't see anything that sticks out to me in my factorio-current.log
Installed on server and synchronized mods, haven't changed anything.

Same as everyone else here, was working fine in single player, then installed the mod on my dedicated server and was getting ready to update my trains just to fail to join 😢

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-Automatic_Train_Painter

from client log file

  94.923 Error ClientMultiplayerManager.cpp:1072: mod-Automatic_Train_Painter was not registered for the following events when the map was saved but has registered them as a result of loading: Custom event (ID 351), Custom event (ID 355) and Custom event (ID 356)
  94.924 Error ClientMultiplayerManager.cpp:99: MultiplayerManager failed: "" + multiplayer.script-event-mismatch + "
" + "
mod-Automatic_Train_Painter"

Having the server save and restarting the server and then joining seems to have worked fine, tho I'm worried it might break 😄
Probably some event listeners need to be registered on init as well and not just on load :)

same here

Have played it fine in multiplayer since this initial crash, have the server save after mod is iniitalised and then restart and anyone loading should load the same custom event ids.

is this ever going to be fixed ?

+1