After a few try playing ZA3 Fatal Canyon Expert or Nightmare difficulty, I think I now understand the cause of the bug or the bug itself that it has. The bug is actually the 3rd special mission that now appears in Sniper Boss stage. That shouldn't be there. It has no description in it but just numbers. It's actually the final installment of missions in the latest map update of ZA3 FC. It's a special mission where you have to beat sniper boss Wesley Longbill under 5 minutes in order for you to play it. In this special mission you have to defeat the Longbill Brothers, though I don't have the full details on this but that's much about it. So currently, if you play ZA3 FC and you defeated Wesley Longbill under 5 minutes, it will trigger the special mission to activate, but since there's no one there to defeat rather it's practically an empty stage/mission you will just be stuck there for the rest of the time until you decided to quit, however if you get to defeat Wesley Longbill beyond 5 minutes time you'll fail the special mission and consequently you will be transported to the final Stage of the map, that is to defeat Uranus. This is the strategy as well to get past thru that map, defeat Wesley Longbill after 5 minutes to deliberately fail the special mission. Thus I conclude, the game developer must remove that bug parameters (3rd special mission in 2nd stage) of the ZA3 FC map otherwise this too much of an inconvenience will continue. I hope in this forthcoming maintenance they will.