I see many issues done by users because they switched screens not correct.
This below is now just one of many other solutions:
If you dont open/close screens correct your app will get possible runtime errors.
Possible errors: (example)
Unable to add window -- token [email protected] is not valid; is your activity running?
Iam sure you don’t want that.
Then please do it in the future and switch screens correct.
General Tips and Tricks for App Inventor/Makeroid
The recommended method of switching screens in App Inventor