OK. I have done the factory reset. As you say not as major a deal as I had thought!
Of course, now I need to wait a while (48hrs or so!) to check that all remains OK. If it remaisn OK I will come back and mark it as the solution.
Thank you for your assistance.
See how it goes. The problem with firmware upgrades, is that there may be changes in the configuration file which are needed by the new firmware. By doing a factory reset, you load the default configuration that goes with that firmware.
Many router manufacturers recommend a factory reset after a firmware upgrade, to avoid such issues.
I can see that. However, when the update occurs automatically overnight how are you to know when it is necessary? Only when it goes pear-shaped!!
Hopefully it is better now and as you say we shall see.
All OK after a week so it looks like that sorted it.