adb – Boot Loop with the old CyanogenMod: multiple files can not be created

My old One Plus One suddenly refuses to start without any change on my part. The operating system is CyanogenMod 11. The device is rooted and has installed TWRP and debugging is active. The symptoms are the following:

  • Once lit, the 1+ logo is displayed briefly as usual.
  • Then the CM logo that looks like a turning screw is displayed indefinitely.

I can boot to the TWRP recovery mode. However, before attempting a factory reset, I would like to make a backup with TWRP. This works fine for / system but fails for the / data partition. There are error messages Unable to stat 3 files /data/data/,
Y /data/data/

When I try to back up with adb, I get stuck at the stage where I am supposed to confirm the backup on the phone itself.

Is there any possibility of enforcing the adb backup and omitting the confirmation? Any other means of backing up the application date before attempting to restore factory settings? Are there other forms of backup I could use?

I'm also thinking about taking all the / data / data directory to my computer through adb. Would this be a viable option to restore the data later?

Thanks for any help!