workaround fix is to use the liner tool and make a new line. But instead of left click to confirm you right click to cancel it, and it will remove the reported marker.

Same, I fix it by saving and loading, but it appears again as soon as I delete one or two reported markers.

unfortunately I have the same thing happening, the line tool workaround doesn't work for me either. no other map-related mods active and I frequently clear datasheets and cache as well.