1. Test your damn product before it goes live.
2. User feedback, user feedback, user feedback. Things like the confusion of the use of "app" (vs "website") and the lack of http->https routing scream of things that a developer would think are "obvious" but even the most basic user testing would reveal early on.
3. Stealth mode can be trouble. This may be a controversial opinion but I've learned to believe more and more that "Surprise! We're here!" approach does more harm than good. There are limited circumstances where this is not the case (situations where knowing the existence of a project can damage that project) but I emphasize limited.