I'm not sure if this is map related, or what's causing it, but after a round ends, all players are slayed at round start, and this will keep happening permanently until map change.
This is not guaranteed to happen.
I tried peeking at the train's hammer editor and could not find anything. I cannot think of any plugin that slays the players.
Edit: It appears that players are spawned to the void.
Removing all plugins except playercommands and slaying all players doesn't solve it, maybe a plugin moves "info_survivor_position"? Maybe Glubtastic3 does it? Also happens in that finale.