Zombies do nothing after spawning from the second spawner, I tried making a new map but still stuck with the same problem.
 
zombie spawner:
targetname: start_zone_spawners
script_noteworthy: zombie_spawner
script_forcespawn: 1
count: 9999
spawnflags: 3
 
 
zone:
targetname: start_zone
target: start_zone_spawners