Performance Condition

The basis of the PC is your maxHR setting in the device. If You reach the ~70%MAXHr then the PC message is popping up. So i think your MAXHR value is too high in the 530, the 70% is an easy-moderate ride, so usually the PC is always shown, except on recovery rides.

Of course it could be HRbelt issue too, we should see the raw data (FIT file, not GC link) for conclusion

I look in GC. I don't know....but the values are wrong....I always use the zone from "Allen, Coggon"

Think so!

Meanwhile i guessed what was the problem, DISABLE THE AUTO-DETECT MAXHR in both devices, if You have a faulty HR belt (or even a false high HR value, like 255bpm), these devices replace the good/real maxHR value with this false extrahigh value and zones will be wrong and the PC wont work neither.

Well, i think the problem is not the belt. 6-7 Weeks ago, Garmin exchange my Fenix 6 Pro because the wirst-HR-Sensor was damage. When setting up the watch, the value must have been adjusted?

If the Physio TrueUp is enabled in the new one then You dont need to reconfigure the replaced watch again . Honestly i dont like these "automated" things i always turn off every "auto" features and check every settings manually. Sometimes a firmware update can ruin everything...

I have found the mistake. In the time Garmin Replace my Fenix6Pro, i used the FR645M from my wife.....I load up the the single activity to my account. After that TrueUp change the values  

Great!