It happened when loading the map, which may have been saved with an earlier version.
When I hosted, my friend at first failed to connect with a message about mods being different despite the version being the same, so I deleted and re-downloaded the mod, then this happened after I reloaded the original saved game.
Could be a remnant in the save file that's causing an issue, or something else.
However, I made a new save after getting the message, and loaded that save in latest version as of today, and I'm not getting that message now.
The problem might be resolved then. Unless it's an issue that persists... I'll get back to this later if any issues pop up again.
