Login URL changed from mydomain

A few days ago, my usual login method (mydomainname.my.salesforce.com

) started failing with "Problem Verifying Your Identity" and no choices (except contact your admin). 

I am System Administrator, with a passkey stored in my pw mgr.  This has worked until a few days ago. 

If I visit

, my passkey works like normal. 

What guidance did I miss among all the elevated users info recently?  What is the best practice now for a mydomain login URL?