SIDs in Active Directory GPO
Yes, you are correct, SIDs that are shown in numeric form typically mean that they cannot be resolved by either your local machine or your domain controller.
Download SysInternals' (Microsoft's) PSGetSID tool (here) and obtain the SID for your domain:
psgetsid.exe <DOMAIN_NAME>
Have a look at the format of a SID on wikipedia, to see if the domain part of your unresolved SID matches your domain's SID.