It's alpha. This is exactly what they're testing. They have (triple digit number) of players, plus mobs / NPCs, and they're testing the limits of the zone capacity. I'm assuming all of the things you've mentioned are side effects. They said they're fixing the issue for the next week and then continuing the testing for 5 days after that, and then opening it up for global alpha.

Don't criticize like the game is the finished product. They're just under half a year from release.