What's your best guess as to their cause, EG?
Bear with me as I set some context ...
I think a lot of the sightings in more recent times have been misidentified artificial lights - e.g., from trains or automobile traffic. The Brown Mountain area is permeated with settled areas that produce a lot of different light forms - e.g., the nearby towns of Lenoir and Morganton. This, plus a reasonably organized series of sightings and interviews, led USGS investigators to conclude the lights were of non-natural origin (perhaps reflected / refracted in addition to observed directly) back in 1922. The reprinted 1922 report can be accessed at:
https://pubs.usgs.gov/circ/1971/0646/report.pdf
I mention all this not because I believe artificial lights account for the entirety of sightings, but rather to note that a lot of 'filtering' has to be done to determine which observed lights may reasonably be taken to be anomalous. The necessity for such filtering has steadily increased over the decades with increased settlement and associated illumination in the area.
Still, there's one fact or factor that seems well-established throughout the history of the sightings - the lights are almost always seen from a distance. In over a century of sightings there are very, very few claims of anyone observing the lights up close (e.g., at a distance of yards within a forest). This consistent feature suggests the truly anomalous lights involve something to do with atmospheric conditions to become visible or to appear as anomalies.
I've never witnessed a credibly anomalous light there that moves at anything other than a slow, lazy pace (if at all). I've only rarely seen a credibly anomalous light that rises so far above the ridge line as to be backgrounded against sky alone, though I've often seen lights rise far enough to ascertain they were hovering above the ridge line. Note my allusion to hovering. I've only rarely observed a credibly anomalous light move laterally, and even then not by much.
Similarly, I've only seen occasional credibly anomalous lights that were clearly situated among trees.
The mountains in that area are largely granitic, with considerable quartz content and inclusions of metallic minerals (especially iron). Detectable magnetic deviations (vis a vis the compass) are common but relatively localized throughout the area.
Having said all that ... IMHO the credibly anomalous lights I've personally witnessed are localized, generally limited to vertical movement, and strongly correlated with peaks and ridges. If there's a natural explanation I suspect it has something to do with illumination of possibly ionized air above transient hotspots of electromagnetic disturbance - possibly resulting from piezoelectric effects in the surface rocks.