Enemies keep gathering and stumble upon each other

I'm making a 3D zombie game using AITherdPersonController from the standard Unity Asset. The problem is that when zombies chase after the player, especially when the latter runs around them, it looks like they "forget" what to do and begin to bunch together running towards each other. After some time they "remember" what they are supposed to do and begin to chase the player again. I've googled the entire internet but haven't found the solution. I've been learning Unity, so...
I record the problem. You can find the link below.
https://drive.google.com/file/d/1oklpaPPFU7gL3uLOWpzvTDp0GVJBuV_f/view?usp=sharing