Could you expound a bit more on your question/comment?
First, what is your app ID and the Hub ID of the account your app is connected to?
Are you subscribing to a particular contact, company, or deal property which then changes but doesn't send a notification? If so, please share a link to the webhook subscription in your app and include links to a few objects where the property value changed but no notification was received.
I can totally see the use case for an object association change web hook. I’ll pass this feedback along internally, and if you have the inclination I would definitely encourage you to check out the Ideas Forum on the HubSpot Community. There, you can post/vote on ideas for the product to be seen by HubSpotters, partners, and other customers alike.
It’s currently not possible to subscribe to a web hook for deal<->company association changes. The current available web hook subscriptions are related to creations, deletions, or property changes.
If HubSpot could create a simple web hook that was sent for any change to an Object (Deal,Company…) that included the changed Object Id. That would cover what I need and other ‘holes’ in the currently available web hooks.