Here another bug I encountered:
Upon finishing a treadmill run, I was unable to end (save) an activity - it simply did not respond. I think what happened is that I started to walk after pausing the activity but before saving. It popped up an alert that said something like “motion detected”. And then, even though my intention was to end and save my run I was unable to do so. Eventually I restarted the activity, and then I was able to stop and save it again.
Also, with regards to the HR graph bug I mentioned above, that happens every single time in my custom trail run activity. But there isn’t such issue in a built-in strength training activity that also has a HR graph data screen.