I have a similar issue. I created a webhook in my application to be triggered when a companies lifecycle stage field is updated. I created the app, granted contacts rights, which should be sufficient for company changes. Finally I installed this webapp succesfully in my dev test account. So basically all steps as in the docs.
But I do not receive any data in my webhookurl when I change the Lifecycle stage property of a company.
Second thing I find odd: When I create the webhook in the app and then go to the menuoption monitoring->webhooks, it says "No webhooks to be found." Even though the webhook is tested and active.
Then, when I click the "Create webhook subscription" button, I go to exactly the same spot as where I created the webhook in the first place.