Hi Hellenjenrau,
How did you get on with the chest strap.
I have the same experience regarding lowering HR when going slowly up hills. I don’t believe a wrist HR monitor has that level of innacuracy. I realise it’s not exact but it always backs up my experience and was comparable with a machine at the hospital when I did a stress test.
Like you I felt exhausted running up a 1 in 7 hill (into a strong wind – Scotland) and was concerned to see my heart rate dropping. My pace was very slow and cadence low.
Did you find any answers?