Hi Dave … Yikes! I’ve got them too. If I move slightly away, it/they disappear. But I also have a column of trees going up. Difficult to see in my screenshot, but as you move around, there are many trees in the invisible column. I’ve had the Berner’s Bay Cabin in there for 2 years and have never seen this before. If I turn off RTMM, they are still there. Well, there goes tomorrow! 
Something to figure out. Thank you for bringing it to my attention. (Berner’s Bay Cabin is at 58.76982, -134.9333)
Update:
Clue #1, I turned off all RTMM, and the columns are still there.
Clue #2, ORBX Alaska Mesh turned off, and the columns are still there!
. . . . .I think it is a sim problem at this point.
