Issues trying to understand and debug simplesamlphp error Simplesamlphp used to work on the site. Something changed and now it does not.

The IDP remote config has been verified, including the cert
The SP cert and pem in the simplesamlphp/config folder have been verified
All the required settings show green on the admin page
When the ACS URL is entered as a test, a JSON file with the metadata is downloaded

All there seems correct. But when a user attempts to login, the following is thrown into the log file. I note that despite the entry about the candidate having :443, the URL with or without the port results in identical json.
This is Drupal 8.9.6, PHP 7.3.21, simplesamlphp_auth 8.x-3.2, simplesamlphp 1.18.8

simplesamlphp ERROR [ffdf5e0102] SimpleSAML\Error\Error: UNHANDLEDEXCEPTION
simplesamlphp ERROR [ffdf5e0102] Backtrace:
simplesamlphp ERROR [ffdf5e0102] 1 /mnt/www/html/mysite/vendor/simplesamlphp/simplesamlphp/www/_include.php:17 (SimpleSAML_exception_handler)
simplesamlphp ERROR [ffdf5e0102] 0 [builtin] (N/A)
simplesamlphp ERROR [ffdf5e0102] Caused by: SimpleSAML\Error\Exception: &gt; This SP [https://admin.mysite.gov/simplesaml/module.php/saml/sp/metadata.php/default-sp]  is not a valid audience for the assertion. Candidates were: [https://admin.mysite.gov:443/simplesaml/module.php/saml/sp/metadata.php/default-sp]
simplesamlphp ERROR [ffdf5e0102] Backtrace:
simplesamlphp ERROR [ffdf5e0102] 4 /mnt/www/html/mysite/vendor/simplesamlphp/simplesamlphp/modules/saml/lib/Message.php:718 (SimpleSAML\Module\saml\Message::processAssertion)
simplesamlphp ERROR [ffdf5e0102] 3 /mnt/www/html/mysite/vendor/simplesamlphp/simplesamlphp/modules/saml/lib/Message.php:640 (SimpleSAML\Module\saml\Message::processResponse)
simplesamlphp ERROR [ffdf5e0102] 2 /mnt/www/html/mysite/vendor/simplesamlphp/simplesamlphp/modules/saml/www/sp/saml2-acs.php:141 (require)
simplesamlphp ERROR [ffdf5e0102] 1 /mnt/www/html/mysite/vendor/simplesamlphp/simplesamlphp/lib/SimpleSAML/Module.php:260 (SimpleSAML\Module::process)
simplesamlphp ERROR [ffdf5e0102] 0 /mnt/www/html/mysite/vendor/simplesamlphp/simplesamlphp/www/module.php:10 (N/A)
simplesamlphp ERROR [ffdf5e0102] Error report with id 86f8550b generated.
It turns out that the issue was the entityID on the authenticator end containing the port number, and the default entityID provided by simplesamlphp not so. Having the authenticator change their config entries, dropping the explicit port reference, resolved the issue.