@adoran2 That does sound exhausting. That's a pretty good cadence increase just to stay at the same power output. All I can think to try would be some experiments at different outputs to see if the drift is consistent -- which involves a lot of work and time plus uncertainty!
@alans The heart rate increase shows that it’s definitely harder work for me by the end of the ride, which is no bad thing I guess? But that harder work might just be a higher cadence. The trouble with trying different power outputs is that it still won’t prove what the cause is.
@adoran2 Right, it's not necessarily bad, but it's definitely a different kind of ride than 'just' endurance. I was thinking with the power output thing that maybe it could help isolate the problem or give you more data that you could take to tech support, which sort of feels like the ultimate destination for this.