I have recently acquired a second hand but well working intel NUC i7, and have bought a new Samsung 970 EVO 1Tb M.2 disk to put into it. I have noticed that every once in a while, say once every two weeks, my disk has gone into read-only mode when I check on it in the morning (this unit is on permanently). When running fsck from 'safe' mode, fixing the disk only finds and fixes orphaned inodes, there are no bad blocks. After the first two times this happened, I had the disk replaced, and put in a surge protector because my electrics are a bit iffy and thought this might be the cause. The replaced disk with the surge protector shows the same behaviour.

Could it be something to do with the very new model of the type of disk I am using, the second hand NUC, or am I missing something?

Usually it is the filesystem which has been set to read-pnly due to a disk error. Check the system log in /var/log/ for disk errors which will sometimes give useful information, like sense data. It can also be the disk itself set read-only, but this usually requires issuing a command to the disk controller.

Thank you! This helps.