Issues installing SailfishOS updates while "Battery notifier 2" and / or "BTRFS balance checker 2" service runs

As you know I'm a creator both of them...
1. I have Battery notifier 2 on all my devices (Jolla 1, C and Tablet). All devices updated without disabling this service. Jolla C updated from first attempt, Tablet from third attempt ("Cannot install update. Try again later. [OK]"), and Jolla 1 don't remember now (from first or second attempt).
2. Same about BTRFS balance checker 2... Like I wrote above Jolla 1 updated from first or second attempt without disabling this service.

I don't know if this services cause to the update problem or something else... The next update I will try to disable both of them and after this will try to update and count attempts.

Thanks, as this is exactly the reason why I asked a larger audience here: SFOS updates occur too rarely to test these phenomena easily.

On my two Jolla 1 phones, when updating from SailfishOS 2.1.2.3 to 2.1.3.7:

1. On my "testing" phone:
   • I used BTRFS balance checker 2 to balance before updating, then downloaded the update: No "Preparing update".
     I rebooted before intending to install the update, but forgot to switch off "Enable autostart" in BTRFS balance checker 2's settings: I had to start the Download again (which just checks, but does not really download anything, if the SFOS update is already downloaded), still no "Preparing update". I remembered that I have missed this message sometimes at SFOS updates before and that somebody stated here on TJC that he did so too, so I switched the Autostart off, stopped its service via the button in its settings, rebooted and tried again: Now it did "Preparing update".
   • I tried installing the update three times unsuccessfully (as described above and in "Update from 2.1.2.3 to 2.1.3.7 fails on Jolla 1"), then remembered I have seen this before and switching off Battery notifier 2 did help when updating from 2.1.1.26 to 2.1.2.3, so I switched its autostart off, stopped its service, rebooted, triggered the installation of the update again and the update went fine (i.e. with no further unsuccessful tries).
2. As I went out of time that night, I just tried to run the positive tests on my "production" phone while updating:
   • Balanced with BTRFS balance checker 2, disabled its autostart, stopped its service, also disabled Battery notifier 2's autostart and stopped its service, but did not reboot: No "Preparing update" when starting the Download?!?
   • Installing update right after the download finished went fine (i.e. on first try).

I will do some more testing when the next SFOS update arrives.

Hmmm.. I always have "Preparing update"... I also will test on the next update...

This time (from 2.1.3.7 to 2.1.4.14) I experienced exactly the same behaviour again, but rememberd to copy /var/log/systemupdate.log (on the second, third and fourth try to upgrade), though by glancing over it, I found nothing special.

Note, that it takes a reboot after switching off "Enable autostart", hitting "Apply" and then "Stop service" in Battery notifier 2 and BTRFS balance checker 2 to let the SFOS system-update proceed (i.e. switching them off and trying to upgrade without a reboot failed).