I think the delay in background check depend on which country you are form origionally, for example if you are from an unstable musilm country like sudan, yemen, syria, iraq , libya , somalia then expect a looooooong delay ( unfortunately , I am)
If you are from a relatively stable muslim country then it will be longer but no significant delays.
This is the only explanation , Ive seen it with many from those countries. It is not related to the person specific background , as long as you are from those countries then you would be treated that waY for security reasons.