Red Line Swipes Across Screen

Using Waze on iOS via CarPlay. Every now and then I'll glance down and see a red line kind of swipe across the screen. This only happens in the split screen mode. I've never noticed it if I have Waze in full screen.

The line is maybe 1/3rd the width of the Waze window. And it swipes at an angle from left to right.

Has anyone else seen this sort of thing?