One of the issues with firmware 7.6 and 8.0 is that it seemed to import some crazy MaxHR and LTHR settings from Garmin Connect, which could impact what zone the watch thinks you are in.
To fix this, you need to ensure that the correct values are set in GC - you may need to (temporarily) change the method to calculate zones to access these settings, and then sync.
As suggested check your HR settings are correct in Connect and that they have synced in F5. Additionally, make sure your Activity Class hasn't reset itself. Mine went from 7 to 3 on a previous update and this affects Intensity
