When you close your inventory menu, you need to click on 'X' button instead of '...' button.
Don't close your inventory menu through '...' button, your GUI will disappear. Just close it through 'X' button or any back button from your phone. Hope this tip can help you. 🙂
Update : Now I understand the problem. The GUI will disappear if I click on '...' button. If you close your inventory menu with 'X' button, your GUI will stay.
When you close your inventory menu, you need to click on 'X' button instead of '...' button.
Don't close your inventory menu through '...' button, your GUI will disappear.
Just close it through 'X' button or any back button from your phone.
Hope this tip can help you. 🙂
Note : Check MCPE-20786 . It has been resolved.