Child Domain Authentication over inconsistent connection.

When we detach the AD/file server from the network attached to the
parent domain, login authentication can take 5-7 minutes. Also, when an
account from the parent tries to access resources in the child domain,
they get a password challenge and are denied access if trying to use
their parent domain credentials. This occurs even if we explicitly grant
NTFS permissions to a share. Any insight would be appreciated.