After dissecting every area I could think of, leaving it alone and coming back to it on occasion, I finally narrowed it down to an actor data field that was blank for some reason.
In my case it was the Custom Unit Status Frame.
I've been working on a map for some time now, and at some point along the way I started getting the following error every time I fire it up for testing:
UI: Expected File Desc name to lead descName  when relativeDesc is NULL.
Anyone ever see this one before? I've been poking around quite a bit, and I just can't seem to figure out where it's coming from.