Apologies for taking so long to reply. I am experiencing the “authorisation” problem logging in on a daily basis now.
I really wish we could help. I think we've tried many of the obvious things that it could be. I've never been able to duplicate the error you've been getting.
When you get this error, is there any other information or anything else that we could try to use to diagnose the issue. I wonder if you'd be able to access the browsers console window. I think you said you were on a Mac. I don't use a Mac and are unsure how much we'd gain from this, but it is worth a try.
https://support.apple.com/en-gb/guide/safari/sfri20948/macWhen you get the error, try to access the console and we see the log messages.
https://support.apple.com/en-gb/guide/console/cnsl1012/macIt’s really frustrating. I wish there was someone who would reply and help me sort it out.
Always ready to help a damsel in distress.