Changing the Content Approval settings of a list can cause an issue with Sintel Forms
Turning on and off the Content Approval setting (List Settings ->Versioning Settings) can break a form you have configured.
This issue is caused by changes that SharePoint makes when you enable and disable Content Approval. When you enable Content Approval SharePoint automatically sets the default ListView to something other than ‘All Items’ however if you disable Content Approval SharePoint again it does not set the default ListView again meaning that no view is marked as default one. The solution for this issue is to simply set a default view in the List Settings again.