I've seen plenty of Infected do this
Where they crawl, in the crouch position endlessly in a direction and won't aggro or chase after you.
They also can crawl endlessly in the prone position, and not aggro, but they still hit you, if you get in their way, when they're in the prone position.
Zombies/Infected are also going through hills, and terrain & getting stuck under them. (like the hills at the airfield)
Especially when they're in this endless crawl, they seem to morph through every single object (I locked a crawling zombies in a container, and he just morphed through the other side)
Stress test #51 on a NE server 2018-10-20