Hello, I'll take a look at it soon thank you for throwing that together, but I noticed in the spawned event in which you were saying might be the problematic one I saw that you're Erasing the event instead of unspawning it. I'm not sure if that's what's causing the problem but if you do erase a saved event then when the event is respawned it would be respawned as an erased event whenever you return to the map.
If you no longer need an event you should Unspawn it and remove the save data as well.
From what I see here it appears to me that this event would be getting respawned as an erased event, this is assuming that it's also a saved event itself, so even if it's not causing this problem it's probably unintended behavior occurring nonetheless. If you're spawning a saved event, interacting with it and erasing the event after it spawns another saved event then you're not actually removing any saved data so when you return to the map any erased events would be restored as erased events and might cause unexpected behavior. I'd say a great starting point would be to check your events and make sure if you're spawning them then you'll be unspawning them to remove them, and if you no longer need the saved data then be sure to remove that too in the plugin command.
I did run some tests in my demo project earlier after seeing your video and tried to do all the things you did in your video, just doing it manually without your plugin, I was able to spawn a saved event and set a selfVariable value to it, then i saved the game went to another map saved the game to another slot then changed the selfVariable value from the other map and then returned to the map with the event and it didn't crash. I kept trying different things to try to get it to crash and couldn't get it to happen.
One other note is the way his Self Variable plugin is structured there isn't really much of a reason for it to conflict with a spawner, as long as the spawner can retain the eventId, such as saved events, there isn't much of a reason I can see which should cause a conflict between the plugins. He's just storing data and tying it to an eventId on tied to game map ids and offers you a convenient way to access it and modify it, it's done well. He doesn't seem to be doing too much with Game_Event that would cause any problems.
Like I said though I'll be taking a look at the project you've provided soon
Let me know if this ended up being the issue, hopefully it was something as simple as this :)