You not flashed no verity opt encrypt 6.0 zip after flashing oreo backup
My guess is that after restoring system and oreo boot img the phone gets encrypted. So you've to format internal storage, then flash no verity zip and then magisk
When you came from stock, you have to wipe all the partition (Format Data) before Mount a blank partition data (like /system). I think it's the encryption issue.
U have debloated a lot of apps in a single reboot.
Here you go- https://mega.nz/#!AYMyTYJb!G2hF1aO03ZB4rMUcNP18uem_JSKv6PftOQsikhTKpew
Install all apks and try pairing now. It will work.
Tested in my Gear S3.
Modem is included with boot image.
Remove one folder...there is one too many