After upgrading to 12.6.4 today the auto-generated ssl cert files in /etc/gitlab/ssl all have the wrong file name.
the cert files are name with the internal server FQDN instead of the external_url parameter.
As they have the wrong file name, nginx wont start due to the error:
cannot load certificate "/etc/gitlab/ssl/.crt
The cert is valid for the external_url so once we rename the files in /etc/gitlab/ssl/ to the correct file name nginx starts and all works as expected.
Until 90 days later the cert will expire.