We have a performance improvement plan in the works yes. Not sure what you mean by map disappears? Is it not only first time you start up and might have to click the "load map" on a slow network?
Are you running IOS7 or 8? If you're on IOS7 you could try running from the home-screen, should be less resizing then. Safari on IOS8 is odd in that it somehow always tries to hide/show the browser buttons much more than in the previous version, which causes "jumpiness"
We're trying to improve this.
You could also try the Chrome browser and see if it "feels" better for you (we'll strive to make Safari work fine of course!)