Not exactly sure what happened.
Kicked a guy impersonating yoyo who wouldn't stop spamming. Next round later I see cts killing terrorists and no zombies were spawning. I checked the console for any commands going off and I didn't see anything. Ztele wasn't working either. It looked like zombie mod was just turned off; I switched the map hoping it would fix it. The server was unusually laggy during that map too; several moments of unable to move for anyone.
Next map, zm_rooftop_runaway had low gravity. It was at 615. I noticed when I shot a poison into the air and kept him up there till he flew out of the map.
This was about 3:45 pm central time.