I cannot login after Windows 10 update, says "password is incorrect"

I have, essentially, the same problem, but only on one of my two PCs that have (as far as I know) the same account.

Whenever there's an update, I find that the password I've set up is 'incorrect'.  Trying to then go via 'Forgot Password' fails, as it says it 'can't get through just now', no matter how long you wait.

So I do a push-button reset on the PC.  I can then sign in with my known password, but it tells me that it has reverted to the previous version of Win10. That password works fine, until it does the update again, which it tries to do quite soon after, as you would expect because the new update has been uninstalled. Then the same problem starts again.

While still in the 'previous version' I successfully used the known password to uncheck the setting that requires a password to log in  -  this PC is at home and only used by me, so I really don't need a Microsoft password-protected log-in. But after the next update, it was as if that setting was ignored, and it asks for the password. Hitting Enter (ie no password) has no effect, and the known password is 'incorrect', yet again.

None of this occurs on my other PC, where I've successfully cancelled the need for a password.

Be careful about the keyboard language config.

My wife changed the keyboard language and I did not notice so the password always wrong. Until click the 'show password' button I find the issue, click the button in the bottom right to change keyboard language and able to login again.

Usually, keyboard error is a primary source of this problem. Besides the caps lock, there can be a num lock on. The keyboard could have hardware and configuration issues.

Use the onscreen keyboard instead of the usual hardware. You can activate it by clicking on the Ease of Access icon on the login screen.   Ease of Access > Onscreen Keyboard is the way to go.

Please take a look at Offline NT Password & Registry Editor

instructions at Lifewire