Data screens auto scrolling during workouts?

I have Auto Scroll turned off under Run Settings. But despite that, I've noticed that when I'm doing a saved workout (for example, an interval run), the data screen stills seems to sporadically auto-scroll away from the current step screen. It doesn't seem to happen according to any rule that I can figure out. For example, it will stay put for the first 15 minutes of the workout, and then decide to act up. I also have key vibrate turned on, so if I was accidentally pushing a button with my wrist or something, I am pretty sure I would notice it.

Has anyone else encountered this?

(This is a Fenix 5S, in case it matters)