If you are working with your app making changes, updating the CMS, etc. and your app all of a sudden won't load or is "crashing"...90% of the time is usually due to something added/deleted/not-functioning on your tabbar.
This could be something that is currently on the tabbar, or something that you were attempting to add to tabbar that is not functioning for some reason.
The first place to start when your app won't load is to "check for errors", on the main dashboard under the "Check for errors" section. This will usually tell you what is going on. I've attached a screenshot of an example of an error that is causing this app to not load.
So in this case the Tab #4 is the reason this app won't load.
Once you fix that tab (by going to that page and figuring out what information is wrong and then clicking the "update" button on that page) you simply need to hit the "Update Live App" button on your main dashboard and it should reload and take that error away. (...Every now and then you might need to hit the Update Live App two times in a row to make the error go away.)
If you are experiencing other issues where you app still isn't loading simply email email@example.com and we will help you get it resolved!