Thanks
@chapjim for the Incognito idea! And
@HitchHiker71 for the (sigh, oft forgotten) cookie deletion!
Apparently when I was whinging earlier about 3 hours late, these techniques would have worked.
I just now reproduced the “something unexpected” at login attempt. Going Incognito
on Chrome/iPad worked(!) and also brought back the reCaptcha I hadn’t noticed was
missing. Then a quick trip to (Chrome iPad) History=>Clear Browsing Data to delete
a week’s worth of cookies, and normal logins now work fine!