I remember having a similar issue with a Sandisk flash drive and a Sandisk microSD a few years back where both storage devices suddenly write protected themselves. I read somewhere that the flash drive had a firmware issue that caused this, maybe the microSD also has a firmware issue.
I would probably send it in to Sandisk for a replacement microSD or return it and get another one/refund.
I would probably send it in to Sandisk for a replacement microSD or return it and get another one/refund.