(cyclinganomaly, this is less about you and more about illustrating the downside of using GPS for track efforts. It's been discussed here several times before, but your 1 video provided proof of it happening. I noticed it happening when I used a Garmin 500 for a while at the track when my SRM was out for a new battery, and noticed that the auto start/stop chime kept beeping when the bike was laying stationary. I looked over and it recored a similar low rate of travel.)
2-4mph may not seem like much, but here's how it may be misleading.
Let's say that you are a decent master riding a 11.9" flying 200M. That's an average speed of 37.5mph/60.4kph. If your computer were reading 2mph faster, you'd see numbers according to that of a 11.3" (39.5mph/63.6kph) ride. If it were reading 4mph faster, you'd see numbers according to an elite world class 10.78" (41.5mph/66.7kph) ride.
The Kilo times would be:
baseline: 1:10.06 (OK for an elite. Good for a master)
+2mph: 1:05.97
+4mph: 1:02.34 (World class. I don't think a US rider has ever ridden a 1:02 at near sea level)
You'd see similar misleading results for pursuit rides. I'm not much of a pursuiter. 4 laps was enough for me
But, I know that adding 1mph to a pace is tough. Adding 2mph is torture. Adding 4 is insane. So, if your computer is telling you that you are riding 2-4mph faster than you really are, then you are being mislead.