I have noticed recently (level 7 during my playthrough) that when walking around exterior cells I have been finding a lot of corpses standing upright.

I think this might have something to do with FCOM, but I have no idea. It isn't really a problem, just something strange I noticed. I think these corpses were killed by Imperial Guards traveling the roads.

Is this common?

It is an engine issue, not an FCOM issue. You'll get that in vanilla as well.

Get a mod like Kuertee's cleanup or Streamline, that will reduce this occurrence.