Problems especially when it is below +15 degrees Celsius. But I found a solution to when the HRM Prp Plus shows a threshold heart rate when you warm up lightly on a downhill and continue like that for 4-8 km so that the last kilometers show correctly. My HRM Tri shows right BPM all the time.
I have tried to start the Strava app on the mobile at the same time and start it as well and it then takes Bluetooth and reads the heart rate. And strangely enough, Ant now gives the correct pulse on the clock.