I've had this exact issue going on for many months. Posted a question about it, but didn't seem like an issue many others were experiencing.
Replaced graphics card, fresh OS and SONAR install, Win10 upgrade.... didn't get rid of it either.
For what it's worth, I've traced my ghost lines to this scenario:
Track View/ All Track Visible ( Folders as well as individual tracks)
Pull focus to a single track or group of tracks, lines appear that are graphic remnants of how the clips and folders were represented in the prior view. I've repeated this on several projects and the ghost lines are definitely connected to the visual representation of the previous view. The layout and shapes match up. ( I'll post pics if needed).
You might test this out to see if that's your situation as well.
If so, maybe there's a common MB, ram or graphics card in our systems that don't play well with SONAR's GUI implementation.
BTW, I've seen no correlation with project size or demand but will look into that.