Zombies getting stuck on Grim Pantry + No Adept

UgyBoogie

Was playing Nemesis on Grim Pantry and every time the Zombies walked up the ramp of the elevated platform in the corner of the map, they just stopped moving. Might be in conjunction with a hook being placed right at the top of the ramp. But the zombies completely stopped moving there until I killed them. When they respawned, they walked back to the ramp and got stuck again, both of them.

Also, got a Merciless Victory with only using the Nemesis' perks and didn't get the Adept achievement.