There are several cases that have been causing trouble for invidious, such as the mushrooms on the Greenway, or the snakes and centipedes in Scorn's underground. While it's hard enough for the server to keep up when blasting cone spells into mobs, it's made much worse on tiled maps, as monsters can cross tiles and keep the entire mapset from resetting properly.
It would seem wise to limit the number of monsters that can spawn from slimes, snakes, mice, etc.
One possible solution would be to make the generator_generated flag pass to items created by a generator. Then, the arches could simply have the generator_limit flag set.
A possible solution is to use generator_max_map. But, this seems oddly broken, in my testing the monster would vanish almost immediately, even if the limit was not yet reached.
Not sure about other places, but in scorns old city, perhaps some kind of "no monster pass" floor for the edges of tiles or regions. Possibly by monster type? IDK, not ideal, but it is way to easy for a character to have old city play ruined by overwhelming snakes and centipedes.