not a real issue, a false error message in my opinion. I see it under Linux, where Hyper-V is thin on the ground.
it seems that the Duplicati code is not even handling the 429 error code. Yet the official statistics seem to show that Backblaze is the most used proprietary backend after GDrive (although the Duplicati stats also show that the Hubic backend is still used, so their reliability is not obvious…)