I went out round 0815 today and noticed that my 3G/4G connection had suddenly vanished!! Hotspot WiFi and the phone connection are not affected. I tried all the usual fixes including ALL to 789922. What's going on??
Unfortunately I'm not sure how I did it, but the experience did force me to learn about what to look for in settings. I also learned that wifi and 4G don't appear together top right on the status screen - it's one or the other.
I also learned to put the phone to sleep straight away when I'm not using it, or you can bugger up settings just by carrying it around.