What version of the Bot Libre app are you using, and what version of Android. and what brand of phone?
Do you mean the green button at the top of the Browse screen? That just tracks that last bot you connected to. If you browse "My Bots" you should still see your bot (ensure you are logged in).
How stable is your Internet connection?
Did you download the app from Google Play? Make sure you click on "Report" on the error screen when the app crashes.