Hi,
I think I'm missing really basic things, but nevertheless cannot advance without your help. Very simple scenario: I have a PowerApps form that was created with the "Customize with PowerApps" button from Sharepoint list. Then I add another screen to the form. Whenever i press the Save button on this another screen, the form fails to save:

with an error "There was a problem saving your changes. The data source may be invalid."
However when I press Save button on the screen automatically created, the button works fine.
None of my columns are set to Required in SP list settings.
Would appreciate any suggestion!
Sasha