These notifications are usually sent when someone changes a resource's availability in the Resources section—bookings may not fit the new schedule once the availability has been changed.
When someone tries to make this type of adjustment to a resource’s availability, they’ll see the following warning;
“Are you sure? Bookings in the future that no longer fit the new schedule will be deleted. This could also result in some repeat bookings being split up."
If the person making the change clicks OK and some of your bookings are deleted as a result, you will receive a notification via email.