Actually I just tried this on mountainous areas and areas with fewer buildings and it seems to work fine, however, whenever there seems to be cover lying around such as a city block or something is when there seems to be a problem. Not only do they take long to move, but they also have a hard time ordering administration of first aid.

I think this bug only appears in more complex missions with many units. And MadocComadrin actually pointed out something of interest as well. I've noticed that aswell! This may contribute to slower healing time

Just try to give an ai a pistol in the editor and try having him move or better yet, lead, and watch him wait around not even looking around