It seems to depend on how long the device was offline. After a short time, the text notes are still there but all the attachments are gone. After a longer period of time, the configuration fails, and an empty database appears.
This seems to be related with another issue I just noticed. In older versions, for each notebook, there was a button by which you could activate and deactivate an offline mode. With offline activated, all content for that notebook including all file attachments was downloaded to your device. So, it was always available independent from a data connection. Here, a screenshot from version 8.13:
In version 10.x, that button is gone: