This photo will explain.

Sync changed, or maybe the sync was afk/not that great

The trap is usually delayed lately, and mice no longer have to wait before it spawns because you can just grab the cheese and go before it gets you

mmm well I'm not sure, it was bizarre. also hello draco i love you

Draco is right. This happens when the sync changes. And the trap is not delayed lately. Together with all the other vanilla map changes, the timer got randomized to a certain degree to make it less predictable.

sometimes it seems to happen on map 58

where the trampolines are usually duplicated before the countdown is over

As explained, map spawned shaman items can get duplicated if the sync changes. Though technically a bug it's a very small issue which has been around since the game's release.

It's highly unlikely that it will be fixed.