I would recommend a hard reset just to make sure there is no traces left.
Here is something that could help with that message removal https://www.qnap.com/en/how-to/faq/artic...y-deadbolt
Here is something to decrypt data https://www.qnap.com/en/how-to/faq/artic...yption-key
Some more guides
https://www.qnap.com/en/search?tab=resource&pages[resource]=0&query=deadbolt
https://www.qnap.com/en/security-advisory/QSA-22-19
I hope this helps.
Here is something that could help with that message removal https://www.qnap.com/en/how-to/faq/artic...y-deadbolt
Here is something to decrypt data https://www.qnap.com/en/how-to/faq/artic...yption-key
Some more guides
https://www.qnap.com/en/search?tab=resource&pages[resource]=0&query=deadbolt
https://www.qnap.com/en/security-advisory/QSA-22-19
I hope this helps.