Sounds like the same issue people are running into with the checkin-checkout Web service.
If you need a quick fix, I recommend using qRules SubmitToSharePoint list command but it will require that the sandbox code service is enabled. It is on O365 but performance has degraded a bit recently.
If you are using O365 you could try converting the form to FormsViewer APP which will take an InfoPath form and display it and allow editing and it supports all of the qRules commands without the sandbox.