Huawei Watch GT 6 showing very low heart rate in hiking mode – bug?

I noticed something odd with the heart rate tracking on my Huawei Watch GT 6 while hiking.

When I use the hiking mode, my heart rate almost never goes above 120 bpm, no matter how steep the climb is. I even tried sprinting uphill as a test and the heart rate barely increased.

A friend of mine was hiking with me and I tried his Apple Watch for comparison. It immediately showed 140–150 bpm during the same effort.

What’s strange is that when I go running with my watch, the heart rate data seems perfectly reasonable (usually 150–160 bpm during runs).

So during the hike I switched my watch from hiking mode to running mode, and suddenly the heart rate readings were very similar to the Apple Watch.

Has anyone else experienced this?

Is this a known bug with the hiking activity mode, or could my watch have some kind of hardware issue?