Wiped clean?

A few days ago I installed hass.io (0.54) on my RPI B+, on a 32G sd card. I put in some HUE lights my doorbell and the Honeywell climate control. And did setup ssh access. This all worked.

Yesterday I noticed some strange entries in the log file, that there was not enough space in the database or something like that. Today I started looking in to this. First I did a df to see home much disk space there was. Only 5% used so more than enough free room on the SD card. Next I changed dir to /config and tried looked at the log file with tail homeassistant.log And some a python error nothing to do with the sql error and not enough disk space.

Next thing, I get distracted and come back a few minutes later. I type in ls -al in the shell and I get nothing, or actually total 0 as a response. Nothing there anymore! How is this possible?

What process can wipe all my files?

This never happened to me before. I have more than 20 years experience with linux/unix and have no clue.
in the mean time the complete file system has been wiped. All directories in / are gone. Even most commands are none functional anymore. ps is not working, top is not working.

Only thing that is still working is df

core-ssh:~# df -h
Filesystem                Size      Used Available Use% Mounted on
none                     27.7G      1.3G     24.9G   5% /
tmpfs                   240.7M      4.0K    240.7M   0% /dev
tmpfs                   240.7M         0    240.7M   0% /sys/fs/cgroup
/dev/mmcblk0p6           27.7G      1.3G     24.9G   5% /data
/dev/mmcblk0p6           27.7G      1.3G     24.9G   5% /config
/dev/mmcblk0p6           27.7G      1.3G     24.9G   5% /ssl
/dev/mmcblk0p6           27.7G      1.3G     24.9G   5% /addons
/dev/mmcblk0p6           27.7G      1.3G     24.9G   5% /backup
/dev/mmcblk0p6           27.7G      1.3G     24.9G   5% /share
/dev/mmcblk0p6           27.7G      1.3G     24.9G   5% /etc/resolv.conf
/dev/mmcblk0p6           27.7G      1.3G     24.9G   5% /etc/hostname
/dev/mmcblk0p6           27.7G      1.3G     24.9G   5% /etc/hosts
shm                      64.0M         0     64.0M   0% /dev/shm
tmpfs                   240.7M      4.0K    240.7M   0% /proc/latency_stats
tmpfs                   240.7M      4.0K    240.7M   0% /proc/timer_list
tmpfs                   240.7M      4.0K    240.7M   0% /proc/timer_stats
tmpfs                   240.7M      4.0K    240.7M   0% /proc/sched_debug
tmpfs                   240.7M         0    240.7M   0% /sys/firmware

So looks like there is still something on the card, only nothing I can see or access.
really strange. Will need to powerdown the system and mount the sd card on my linux desktop to check if I can find any clues what is going on. Any help is appreciated.