Strava has no clue how much power you're putting out until you upload actual data(from an actual device that measures it)after a ride. It also, by default uses 220-age so isn't in any way applicable to anything.
Oh sorry, I was replying to OPs
These look odd to me in that how can I be resting for 25% of the way? Granted there are some longish downhill sections but shouldn't my heart rate stay in Z1?