Thanks for the details. I’m afraid the symptoms you describe are highly compatible with the SD card used as internal memory. There have been many, many reports.
So I think it would be highly advisable to “evacuate” the SD card. Unfortunately this will likely entail quite a lot of work, so I’m hoping for at least a second opinion. But my advice would be to bail out anyway, even if the SD card isn’t causing the present problem.
You should read this,
and these (or some of them!)
As to the five-year-old SIM, that’s beginning to be a bit ancient. SIMs deteriorate and can cause all sorts of problems that don’t necessarily appear relevant. They are not expensive, so it might be a good idea to get it replaced anyway, on general principles.