I do drive in the slow lane frequently - and this still occurs. (My go to is to set my cruise 6-9 mph over the speed limit, if passing to smoothly pass and get back over, and spend as much time as possible in the slow lane. )

However - I will say most of the roads I’m on are 2 lanes of traffic. I will have to experiment and see if this doesn’t occur when there are 3 or 4 lanes.

In Southern California the "fast lane" is the medium speed lane, and the "slow lane" is the actual fast lane. It's where people tend to weave in and out of traffic at 15-25 mph speed differentials.