Figured it out.
When I was working on adding SSO with Azure, I could not get SSO to work with the NameIDFormat line in the settings-custom.php file set to the default. I changed it from emailAddress to persistent and was finally able to get SSO working only to discover the issue above hours later.
Changing that line back caused the error to go away and for some reason, also worked for SSO. No idea why it wasn’t working before, but it looks like everything is working fine now.
Thanks