I thought I’d try a couple more flights to help determine the cause. On the first one, I only had the flashing line of lights at and near my departure and arrival airports, so I thought it was some “bleeding over” from lights from the airport. But then on my second flight, I had the problem for the entire flight.
I don’t like the poorer image quality of DLSS, so I’m back to msfs2020 until this problem is fixed.