Used inf. ammo several times and it has always ran fine for me, maybe you hit ZOMBIES DON'T ATTACK by accident and didn't realize it. Trainer worked great on my game (used all of the options at some point or another). Map glitch could be outdated video drivers or another program in the background interfering with it.
I always update both Windows and GPU drivers, restarting the game fixes areas glitching out but still try to use Trainer causes enemy script issues.
I turned off every background apps like you said then tried turn on/off Zombies don't attack option and that did not fix the issue though, same result with run as admin option for trainer app. Even while running the game without the trainer, zombies are just ignoring me. My guess is whole save file's scripts are messed up somehow. Deleting XML file didn't help either.
I guess I have to restart from the very start though.