Hi @Anonymous,
Do you want to reset the Attachments control within the Edit form of your app?
I have made a test on my side (using ResetForm function), and don't have the issue that you mentioned. The GIF screenshot as below:
Set the OnSelect property of the "Reset" button to following formula:
ResetForm(EditForm1);NewForm(EditForm1)
Note: The EditForm1 represents the Edit form control within my app.
On your side, you should type the following formula:
ResetForm(Form3);NewForm(Form3)
If the issue still exists, please take a try to re-create your app (generate an app from SP list data source), then check if the issue is solved.
Best regards,
Kris