Greetings!
When you ran the 'no password non-plaintext-sha256' command, you should have seen a prompt similar to the following:
switch(config)# no password non-plaintext-sha256
**** CAUTION ****
This will remove switch passwords, you need to reconfigure switch passwords later.
Do you want to continue (y/n)? y
Do you want to set new switch passwords (y/n)? n
Did you see that when you ran the command? If you did, did you choose to continue and/or set new passwords?
If you did not see that prompt, could you let us know what software version you're running?