I can’t look right now but it’s likely a similar issue that I ran into regarding gated neighborhoods. Look at the underlying mapping data in OSM database. There’s probably a private gate or road restriction. If so, normal car driving directions won’t route through it. GH will treat the blocked off sections as islands. Or, if the island is all military and too small I think it will get excluded. There’s a config setting for the minimum island size.
If you want those roads to be included, you could maybe lower the minimum island size, and make a vehicle encoder that allows routing through private military roadways and gates.