@Phaedrux
Ah, Okay...
It's not been used for around 3 weeks and the cupboard I keep it in (my printer cupboard), is usually around 15˚c if its door is left closed and not in use (possibly lower than that overnight). It's a double wall to the outside, but a very small cavity, so I've studded this with Rockwool, soundproof plaster board and Tecsound mass loaded vinyl sound proof membrane. Yes you could say this is cold, but it's not damp.
The SD card has been left in the board untouched, not nocked or moved in anyway until last Saturday 25/2/23 when I had the issues.
I'll have to take the board of it's mounting to look and take some pictures of the SD card readers solder joints, and the reader itself.
Like I say, it all of a sudden sprang back into life and I've ran a 10 hour print today with no issues?
Dizzwold.