This only happens on my wifes 2017 T5 (4 cyl). Sitting in bumper to bumper traffic, going @ 26 mph, I am noticing the transmission seems to be motorboating - gear is too high and it cant decide on shifting down.
Good luck in finding any contemporary car that doesn't do this. The shift schedule at low throttle yields low rpm shifts, exactly what it should do and not different from 3 speed auto of many years ago. BUT then the downshift setting is tricky. Too much increase throttle change makes for sluggish response and too little makes for nervous transmission and maybe hurts longevity. I rent vehicles and all these 8, 9, and 10 speed offerings have some speeds that create the indecisive throttle vs. shift issues. It is the one thing that CVT vehicles have an advantage in. The shift schedule of your t6 is different and the supercharger has a HUGE benefit of giving the low RPM torque that makes gear selection less critical.