Once you get in it'll still have to download locations of nearby pokestops and gyms, which is another chance to hang and require a relaunch. Network glitches are not handled gracefully.

On the hang while catching a Pokemon: my guess is it's trying to ask the server if the Pokemon breaks free of the ball. Sometimes when you exit and relaunch you'll have gotten the Pokemon, other times it's totally gone. When the game works properly you get to keep trying, but if it locked up on network issues and made you quit, you don't get the chance. People are understandably annoyed at server issues screwing them out of rare captures.