Thank you everyone for the help. We figured out once the HTTP Content Caching is disabled, it worked. Since we have fibre connection, HTTP Content Caching is somewhat unnecessary.

I had the Unauthorized error on MX 12.24 and after upgrading to MX 13.23, I ended up with this "INTERNAL ERROR: Missing Template ERR_CONNECT_FAIL" error message. Removing all content filtering and reboot does not fix the issue. Not sure what else can...