I've had the same issue a few days ago. I spent an hour or so swapping channels looking for the transporters. After the last reboot, I went and checked, and sure enough, the transporters were there. Either I got incredibly unlucky and someone else kept killing them, the respawn timer is ridiculously long, or these mobs aren't respawning after they're killed, and are only spawned at server startup.
Yeah, I've tried switching channels with no luck, but I guess I'll keep trying and see what happens. Still crazy frustrating though lol. Hopefully I'll have some luck soon.