Another one sample on IndoorRunning

So, pointed line is my cadence (right scale), blue is the "pace" counted by Garmin(c)
i do my 165 cadence (about 7min/km pace) Garmin says me - 5.5 - OK (can be calibrated) - a little slower/brisker - no change. Start walking - will be detected - red dots, 5 sec later i start to run my 7 min/km pace again - nothing happens. After about 30 sec pace still 9.3 min/km, than goes to realistic value. I do a little variability to my run cadence 160-175 - no pace change. At all. Then on minute 7:30 i do quicker - to cadence 180. Garmin gives me unbelievable 3:40 pace. As to me it was 4-4:30 max. Then i go to my steady 7min/km and Garmin give me an 5 min/km pace. What should i say - it is all not the data it is junk.
Edit: my 5 years old va3 do it 10x better