The solution is to clear the site data. For the Chrome Internet browser:
1. go to the Portal website, or as far as you can get
2. press F12 to show Chrome tools
3. go to Application tab
4. in left-hand list go to Storage
5. click ‘Clear Site Data’ (leave all the options underneath this ticked)
6. then try re-loading the site
If using Microsoft Edge it will be almost identical steps, as the F12 tools are very similar.
(Updated April 2025)