Unable to create Group Event Subscription

I have a multi-tenant application that creates event subscriptions. It works fine for over 5600 subscriptions; however, I have one Group that produces the error below.

The code works fine for other Group Event Subscriptions in the same and other tenants. The inputs are verified to be correct, yet it still fails.

I added an event to attempt to trigger some process that may not have completed with no change in results.

There is something wrong with this specific Group Calendar. Any ideas?

Here is my code:

Subscription subscriptionRequest = new Subscription {
    ChangeType = "created,deleted,updated",
    NotificationUrl = NotificationUrl,
    Resource = resource,
    ExpirationDateTime = DateTime.UtcNow.AddMinutes(4229),
    ClientState = matter.Site.TenantId.ToString()
};
Subscription subscription = await client.Subscriptions.Request().AddAsync(subscriptionRequest);

Error:

MessageMicrosoft.Graph.ServiceException 
HResult=0x80131500 
Message=Code: ExtensionError 
Message: 
Operation: Create; 
Exception: [Status Code: BadRequest; Reason: Bad Request]