Based on my experience with upgrading to 1.71 then adding a second SSD for Bitcoin Knots and a NAS connection for Plex Server I would stay on 1.5 until UmbrelOS fixes the persistence issues when rebooting or upgrading that version 1.7 seems to have introduced.
Mind sharing how you did the downgrade, fresh install and then just reinstall everything, or is there some trick to downgrading in place. Have my BTC Knots working on 1.71, after the upgrade broke it, but had to use edits to fstab, mounts in /mnt, and a symbolic link for the Knots /data director all of which will probably be wiped out at the next reboot.
Just flash your SD card with 1.5, the apps and their data are on your SSD