I'm taking a look into it and so far I'm unable to replicate the crash (using Ultimate Event Spawner v1.8). I seem to have both plugins working together even after a map change. I've tried setting self variables on temp events and leaving the map and returning which works (I wouldn't advise using temporary spawned events with these self variables but i tested it anyway), I also did the same with saved spawn events which also worked when returning to the map.
At this point I'm not sure what's causing your problems but it seems like it might be deeper than these 2 plugins conflicting. I'd need more information or a dummy project which crashes (remove all the plugins from js/plugins folder before zipping it, if you decide to do this)