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Looks like the field "Inschrijfgeld" on your cloned form is problematic and it's causing the browser to crash or become unresponsive. I'm not quite sure why, but removing it seems to have fixed the problem. Can you please try to clone your original form again and see if the issue reoccurs? Or if possible, you can delete the mentioned field on your cloned form and recreate it. It seems there's something on this field that's causing the browser to lag base on my test. However after deleting this field, everything goes back to normal.
Please try any of this solution and let us know if the issue persists. Thanks!