Thanks. I’m glad that I am not the only one who thinks this is weird.
The Kickr is a v5 that is connected to an Apple TV. The Quarq is a DZero that is connected to a Garmin 520. The heart rate data shows the same time drift dispite the source for both files is the same (Garmin HR strap), so it suggests that it is due to the recording device and not the power source.
A friend recommended changing the data capture setting on the Garmin 520 from “smart” recording to “1 sec” recording. I will see if that fixes the discrepancy when I ride tomorrow.