I was unable to update to December from November with the 32bit magisk delta patch for some reason. Did you differ from the steps to upgrade at all?
I keep a diary for efforts like this to save time when I need to repeat one. Reviewing, I really didn't do anything different from the OP procedure. However, there was one. I doubt it made a difference. Where I paused between steps 8 & 9 to install the Jan. image, I kept data by editing out "-w" in the script. That logically shouldn't make any difference.
The state my P7P was in: New from Fi in late Nov. Initially updated to the Nov. full image, factory kernel, Magisk stable 25.2 and minimal setup.
My diary: (I referred to HomeBoy76's Guide)
- Downloaded the Jan full factory image and extracted the zips accordingly
- Copied init_boot.img, Magisk Delta custom modified APK & backup-persist.sh files to the phone
- Installed the modified Magisk Delta APK.
- Patched init_boot.img in modified Magisk Delta (edit: be careful not to use stock Magisk)
- Copied the patched boot image file to the Platform Tools folder on PC
- Installed a terminal emulator (Termux for me)
- Opened a SU prompt & ran the backup-persist.sh script (edit: script @ /storage/emulated/0 if you copied to "Home" above so, "cd /storage/emulated/0" then "sh backup-persist.sh" since trouble reported here before)
- Copied resulting presist.img off the phone for safekeeping.
- At this point I flashed the Jan update using HomeBoy76's Guide keeping data
- I rebooted the phone and let the Jan update complete
- Once updated, I shutdown & booted into the bootloader
- On the PC, I reflashed & wiped data: "fastboot --skip-reboot -w update image-cheetah-????.xxxx.xx.zip"
- When finished, I rebooted the bootloader: "fastboot reboot bootloader"
- Then I flashed the Magisk patched boot image: "fastboot flash init_boot magisk_patched-xxxxx_xxxxxx.img"
- Rebooted the phone and allowed the install to complete
- Installed the custom Magisk Delta APK
- I setup Magisk
- Flashed Magisk modules safetynet-fix-v2.3.1-MOD_2.1 by kdrag0n/Displax & MagiskHidePropsConf-v6.1.2 by Didgeridoohan (it took ~12 hrs for "device certified" to appear)
Now I also can see accidentally patching the boot image in stock Magisk could be a tripping point. I have reloaded all my apps and fully setup my P7P. Setup from scratch BTW. Two 32 bit apps too. No problems for ~3 weeks but, it's not my primary phone yet. I can make it my primary in another week, or so, and I'll report if anything changes.