Yeah, solving the monorail sabotage mission appeared to have locked the Strip entrance. BUT I went back later and it worked again.
But the worst bug I had? I had two companions, and at some point, I dunno when, they disappeared. Got stuck on an object or something I guess. So I was without my backup for many many hours. And when I tried to recruit a new companion they said you already have a companion.
Then, when I initiated the final mission, my companions finally respawned with me! I was so delighted! Naturally they got stuck on a flight of stairs five minutes later and never moved again and I had to finish the game without them.