TYPO3 Core

We have a working site with TYPO3 9.5.14. Unfortunately the hosting provider does not support argon2. So we used the bcrypt algorithm as fallback password-hashing configuration so far like this:

$GLOBALS['TYPO3_CONF_VARS']['FE']['passwordHashing']['className'] = 'TYPO3\\CMS\\Core\\Crypto\\PasswordHashing\\BcryptPasswordHash';
$GLOBALS['TYPO3_CONF_VARS']['BE']['passwordHashing']['className'] = 'TYPO3\\CMS\\Core\\Crypto\\PasswordHashing\\BcryptPasswordHash';

After upgrading to 9.5.17 the backend login and the installer login ceased to work.
Login-Warning Mails came up with the message:

Login-attempt from x.x.x.x for username 'yyyy' with an empty password!

BE cache deletion (incl. Browser-Cache and Cookies) did not help.

After resetting the TYPO3 sources to 9.5.14 be login and installer login worked again.