UPDATE: I have since updated to official 5.1.6 via OTA flashed TWRP and Magisk. The backup finished successfully with no sign of 255 error and once rebooted the USER ID and all 999 folders were still gone after the update and switched slots.
Only tested on OnePlus 6 but file structure should be the same on any device running Android O. Must be rooted to grant Terminal Emulator root permission. You cannot remove a user without root.
If anyone has had the 255 error while trying to create a backup file or trying to restore with TWRP. This error pertains to the parallel apps or multi user ID. If you are not sure if you have parallel apps running on your OnePlus 6 or other devices you can do a quick check by go into your Root browser and look in these locations.
/storage/emulated
/data/system/
data/system_ce/
data/system_de/
data/misc/
data/misc_ce/
data/misc_de/
data/user/
data/user_ce/
data/user_de/
If you see any folder named 999 then you have parallel apps enabled on your device. TWRP in it's current form will not allow you to create a backup or restore a backup with parallel apps enabled.
Currently there is only one solution that I have found to be able to delete all of the 999 folders and that is to open a terminal emulator to each of these locations and remove the 999 folders individually. I have found a solution where you can delete the user ID and by doing so it removes all of the 999 folders and not only does it remove the folders they do not return once you reboot your device. The solution is simple so let's get to it.
Install Terminal Emulator from the play store
Open Terminal and type
su
Press enter and grant root permission
Next type
pm remove-user 999
Press enter
Close Terminal and reboot
Once rebooted go back to your Root browser and check the locations listed above to ensure the 999 folders are gone. That's all, Enjoy.
Only tested on OnePlus 6 but file structure should be the same on any device running Android O. Must be rooted to grant Terminal Emulator root permission. You cannot remove a user without root.
If anyone has had the 255 error while trying to create a backup file or trying to restore with TWRP. This error pertains to the parallel apps or multi user ID. If you are not sure if you have parallel apps running on your OnePlus 6 or other devices you can do a quick check by go into your Root browser and look in these locations.
/storage/emulated
/data/system/
data/system_ce/
data/system_de/
data/misc/
data/misc_ce/
data/misc_de/
data/user/
data/user_ce/
data/user_de/
If you see any folder named 999 then you have parallel apps enabled on your device. TWRP in it's current form will not allow you to create a backup or restore a backup with parallel apps enabled.
Currently there is only one solution that I have found to be able to delete all of the 999 folders and that is to open a terminal emulator to each of these locations and remove the 999 folders individually. I have found a solution where you can delete the user ID and by doing so it removes all of the 999 folders and not only does it remove the folders they do not return once you reboot your device. The solution is simple so let's get to it.
Install Terminal Emulator from the play store
Open Terminal and type
su
Press enter and grant root permission
Next type
pm remove-user 999
Press enter
Close Terminal and reboot
Once rebooted go back to your Root browser and check the locations listed above to ensure the 999 folders are gone. That's all, Enjoy.
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