[PROBLEM] No space left on device (but there actually is)

[ulfwin]

Software
XBian version: XBian 1.0 (knockout), kernel: Linux ARM 32-bit version 4.4.7+
XBMC/Kodi version: 16.1-RC2
Overclock settings: default

Hi!

I started to see some unreliable behavior when running "sudo apt-get update". Different error every time, like:

1. Bus error
2. Reading package list taking for ever
3. E: Method gave invalid 103 Redirect message
   

At some point the update seemed to work, and I tried "sudo apt-get upgrade" and after that the SD card is constantly listed as full, even though there's supposed to be plenty of space.

I can ssh without problem, but not much else works (like restoring snapshot). df gives me this conflicting information:

Terminal

xbian@xbian ~ $ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mmcblk0p2 15G 3.9G 0 100% /
none 4.0K 0 4.0K 0% /sys/fs/cgroup
devtmpfs 363M 4.0K 363M 1% /dev
/dev/mmcblk0p2 15G 3.9G 0 100% /home
/dev/mmcblk0p2 15G 3.9G 0 100% /lib/modules
none 74M 300K 74M 1% /run
/dev/mmcblk0p1 68M 25M 44M 36% /boot

The thing is that I've experienced temporary pseudo-disk-fill-up before with Xbian, and I always assumed it to be due to brtfs being experimental. But as far as I understand it's supposed to be quite stable by now.

Prio nr 1 for me would be to restore Xbian, if that possible.[/code] Some understanding of why this is happening would however also be great!

Would anyone be able to help?

Thanks in advance!