The safehouse map is absolutely not under that highway. It's most likely related to placements of other garages. Not fully sure though, since they are quite far away from the highway, and the issues aren't present in places where the garage maps should be loaded.
*this bug happens randomly, too
UPD: The bug doesn't only happen on NFSSA, happens on local servers too.
*this bug happens randomly, too
UPD: The bug doesn't only happen on NFSSA, happens on local servers too.