OK, for those experiencing the same problem Co-Pilot actually came up with the answer.
Go to browser and clear cookies.
Looks like yet another bit of Microsoft flakiness.
I always find myself wondering how my elderly relatives would cope with these constant niggling PC problems.
The answer is they wouldn't, they'd assume it broke and end up paying someone to fix it.
I can think of no other area in life where the user needs to fiddle under the hood so frequently just to keep doing the basics. Even something as complex as cars mostly just work these days.
Makes me wonder why we all put up with this sort of behaviour from Microsoft so often. Any company without their globally over-dominant monopoly would surely have folded by now.
I can see why Applytes always look so smug...