I have a problem. The zombies spawn successfully but fail to target a player. They stand still. Does anyone have a solution to why this is happening?

I had the same problem but then I found that zombie spawner aka script_struct you have to set right KVP values.
Here is tutorial how to properly set spawners
https://confluence.ugx-mods.com/display/UGXMODS/BO3+%7C+Adding+Zombie+Spawners%2C+Risers%2C+and+Window+Barriers
You can also find tutorial on the same page how to set dog rounds right and how to set mystery box location