So, apart from not being able to write on disk which is not formated as internal, even the one that is formatted as such is unusable becuse it keeps disappering from the system.

And the only way to get it back is restart.

It happend a few times already and it seems that it is related to standby time.

EDIT: So, this happens only in REC port on my 50W75C. Solution is to use any other port.