Hey!@Agent_fabulous, @TheImpulson :
I would like to report an issue with this TWRP version (same as with the LR one) happening when using Second Space. This is quite a big issue since that feature really is a great feature of MIUI.
As soon as you enable Second Space, w/ or w/o password (does not matter I tested both), it breaks the backup process at data after just a few % with code ERROR: 255 .
Please see attached picture.
Hope this helps.
I looked into the issue and its due to TWRP not supporting multi/work profiles. You can see the same issue happening on a load of devices here: https://github.com/TeamWin/Team-Win-Recovery-Project/issues/1373.
As it's not a device-side issue exactly, I suggest waiting or removing the folders mentioned in the issue which causes backup to fail.