I changed the google password overnight and the configured kmail imap does not fetch messages from google anymore. Updated the new password in the wallet, removed the gmail account, checked the google app passwords to no avail. Now there is an imap gmail account where in the configuration it says "could not read the password: user rejected wallet access." Though the password is stored in the wallet where it should be.
Problem was authentication request shown. Checked the KMail URL in a logged in browser and Google understood.
Can you comment a little on how exactly you did that? I have the same problem, but don't understand how you solved it...