Bill, Was this outdoors or TM (constant velocity) based? If TM based that might be one of the issues, you can’t use the built in pa:hr measure most of the time but rather the first half of the test HR avg vs. Second half of the test HR average. I would generally expect to see a drift of maybe 10 bpm by that measuring method or more.
My guess is with the info I have is that your AnT is higher than 147 and thus your delta is more than 10%. The other thing to consider is how well you’re recovering whilst training in Zone 2. If your easily recovering after your long days I wouldn’t recommend swapping all your Z2 training for Z1.