Seemingly random drops in health due to terrain?

So while out and about, seemingly at random, members of my party not currently under my direct control will take varying amounts of damage. Sometimes 25%, somtimes 50%, sometimes enough that their portrait will flash in the center of the screen to alert me that they're near death. It seems like, in order to keep at pace with the controlled character, the pathing leads my compatriots through the terrain in such a way that it damages them... which would be far less of an annoyance if they regenerated health out of combat, which they do not.

I searched for others posts on this topic and didn't find anything. Am I alone in experiencing this?