Dim shows a black screen, which uses very little power on the iPhone's OLED display. The map stops updating while dimmed.
More fixes give a steadier position but it trails behind you: about half a second per fix (5 fixes ≈ 2 s ≈ 3 m at walking pace).
The distance grows to the GPS accuracy when that is worse. The climb check stops slow, steep climbs from counting as stops: 3 m in 30 s is a climbing rate of 360 m/h. Lower it if slow climbs still show "Stopped"; it needs a track with elevations.
Removes small ups and downs from total ascent/descent. Compare with Maps 3D PRO on the same GPX to tune it.
Simulated GPS walks the loaded track at 10× speed with GPS noise, a 45 s stop and a 120 m detour. The app reloads when you switch it. Remember to turn it off before a real hike.
"Test loop here" draws a square loop of about 800 m starting where you stand, for a walk-around test.