I don't understand why any Windows Phone would work differently, concerning BAP, when using W10 since you're using the same Software but in a different model/make of Phone and we are fooling W10 into thinking we are using a Lumia not a HTC?
When using your 929, did you set up BAP with the W10 install and if so, any problems with the battery on that phone? Since you have two phones, have you tried fully setting up BAP on the HTC, W10, and then set the backup to "manual" so maybe it doesn't run in the background? Maybe our trying to block it is what is causing the battery drain issue since it gets stuck when trying to run automatically?
I've never used BAP so now I'm thinking I may want to try setting it up fully/properly and seeing if it simply works correctly, not draining the battery, if it is used correctly instead of trying to block it. However, I'm on 15025 and am very happy with this release so I would be very upset if I did a hard reset to start over installing W10 and try to use BAP properly but not be able to get past 14393 like some of you look to be having an issue getting to 15025.