Backup size doesn't seem to be correct I installed TWRP 3.1.0-0 (unofficial, from here) on my Redmi 3S Prime and tried to make a Nandroid backup. I've never taken Nandroid backup before. I have a linux PC. On my PC, I installed adb and fastoot drivers and used took the backup by typing adb backup --twrp in the terminal. My phone showed that the backup size was 9757 MB but the backup.ab file created was only 2.1 GB. Where is the problem? Did I do anything wrong? By the way, I backed up the boot, system and data (excl. storage) partitions. Doing backups on internal storage works fine. So, what is happening?
Seems to be a bug. I tested it on my device multiple times: in GUI mode backup is created fine, whereas console command give this fake.

I already created the ticket on their Github, but they don't read it, as it seems.