Digard
Okay, I had some time, and can confirm 100 % that this happens here. How can I continue debugging this?
For the time being - since restart tvheadend alone doesn't produce this bug - I assume it could be the mount delay. Could it be that the system service tvheadend starts before the external drive becomes available?:
$ df -h
Filesystem Size Used Avail Use% Mounted on
...
/dev/sdc2 6.8G 4.6G 1.8G 72% /
...
...
/dev/sdc1 537M 6.1M 531M 2% /boot/efi
/dev/sdb2 4.6T 2.8T 1.9T 61% /media/me/...
/dev/sda1 224G 67G 158G 30% /var/lib/tvheadend/recordings
$ ...
The files noted as "missing" are available, untouched, and the recordings pop up under "Removed Recordings". It would at least be logical, though wrong, if tvheadend didn't find the recordings on the not yet mounted drive /dev/sda1, to consider the recordings as willfully removed.