Hi @Anonymous,
Could you please share more details about the error message within your app?
I have made a test on my side, and don't have the issue that you mentioned. The screenshot as below:

Within the first screen, set the OnSelect property of the "Navigate" button to following:
Set(varRecordID, 6);Navigate(Screen2,ScreenTransition.Fade)
Within the second screen, set the Item property of the Edit form to following:
LookUp('20181217_case14',ID = varRecordID) /*<- '20181217_case14' represents my SP list data source */
Set the DataSource property of the Edit form to following:
'20181217_case14'
Please check the attached GIF screenshot for more details:
In addition, you could also consider take a try to submit your form data using Patch function instead of SubmitForm function. Please set the OnSelect property of the "Submit" button to following:
Patch(
'YourSPList',
LookUp('YourSPList', ID = varRecordID),
{
Title: DataCardValue1.Text,
Column2: DataCardValue2.Text,
...
}
)
Note: The Title, Column2, etc represents the columns in your SP list.
More details about the Patch function, please check the following article:
Patch function
Best regards,
Kris