If you do have a Nucleus, then indeed the fact that it is now identifying itself as a ROCK device and you are not able to access its Web Administration Interface indicates that the SSD is failing and should be replaced.
You have the option of replacing the SSD yourself or getting it done for you by Roon Labs. The latter route will be expensive, so the Support Team are happy for you to do it yourself (or have a computer-savvy friend or relative do it for you).
@benjamin (of the Support team) has provided instructions on what to do here:
Post your decision on the next steps here, so that the Support Team can either a) initiate a RMA for a repair by Roon Labs or b) wait until you have replaced the SSD and installed ROCK on it; once the Nucleus is back online they can upgrade the ROCK operating system to the Nucleus version remotely.