Mac does not recognize password after upgrade

Solution 1:

In the end I found no reasonable answer to my question. So I decided to set the password (with the method mentioned in the question) to void. Then when the mac is boot the password in no more asked, thus solving the problem.

Solution 2:

Thanks for the post. Just discovered an old iMac which had exactly the same issues as (very nicely) described by yourself.

I think the issue was to do with the update removing wifi connection passwords rather than anything else. If you CMD+R and enter the recovery mode, you can click on the wifi icon and re-enter the wifi connection password. It will all work then too without need to create / edit passwords etc

Thanks Again