Hi, MichaelH.
Thanks for your advise. I have not tried your advise yet, because my computer office is behind firewall. I intend to try it at home.
However, let me tell you this. The unsuccessful login takes place when I type the url https://mydomain.com/wp-admin. When I tried https://mydomain.com/wp-login.php, as suggested in your advice, it worked! I was able to gain access.
Let me just observe for a period of time if this will still work.
Thanks.
Percival