I’m no cardiologist, but just looking at the HR trace on the graph you posted, I’d say it is not the normal shape for the workout.
Take a look at any of the completed Mist +2 workouts and you’ll see traces that are much different in shape:
Heart rate should climb fastest at the start and then start to level off. Your trace climbs linearly for the whole interval. The sixth interval looks particularly strange in that HR doesn’t climb until about half way through. It should also be much smoother than it’s shown on your trace.
I don’t know what any of this really means, whether it a problem with your HRM or something else but it doesn’t look the way I’d expect.