A friend of mine, who if having to venture into a suspect area for his job (repairing slot & fruit machines), used to have an old wallet in his back pocket which had a fiver in it together with a couple of random business cards and long expired store points cards. If he was ever 'lost' this...
Screen shut off but computer runs on. Had problems with my external hard drives connected to the computer when it went to sleep. When it woke up it did not see the drives even though their access lights were on.
I have used Easy Duplicate Finder with great success on daughter's computer on not only photos and videos but music and documents as well. Keep meaning to get to my stuff but tempus fugit! https://www.easyduplicatefinder.com/
Not too sure where you are but if you have a look at XCWeather and click on the Visibility tab you may find it useful. As said mist is very difficult to predict and can be very local based on the terrain and nearby features. The Dew Point temperature is quite important as it's relationship...
When you say 'switch it off' do you mean with the power button on the front or at the plug socket? I leave the power on to my iP8750 (baby compared with your) but always turn it off with the power button.
I found that page as well, BB. Was looking at the last item that seems to say the printer needs a service. It would be interesting to know if the OP has his connected by USB or wi-fi. If USB I would try another cable.