one issue that could be problematic is with DNS if a browser determines it is outside of the "intranet" realm

If the DNS record has a different suffix and is not considered to be part of "Intranet" but instead is "Internet" then the automatic NTLM logon does not take place.

Ask the domain administrator to add the new DNS (local.mycompany.io) to the group policy list of "Intranet" domains. Once group policy is  refreshed, IE, Edge and Chrome will then all allowed automatic NTLM logon without prompting for a username and password