Steps to reproduce:
- Go to System Settings > Forms > Enable experimental interface
- Go to Content > Forms
- Add a Form
- Add a text field
- Make sure the sidebar is still open
- Drag text field to the bottom of the page
User should be able to drag and drop the text field back to its place
Field goes back to its original place by itself and Form freezes completely. See first gif.
Close sidebar before dragging field.
However, by closing the sidebar, when you drag the text field, two lines will be available for you to drop the field. If you drop the field in the second line, Forms will freeze too. See gif #2.