We are making changes to Bitbucket webhooks to improve the reliability and scalability of the infrastructure. These changes should be mostly transparent, however it is important to note that webhooks might be sent from a different range of IPs than they have been in the past as highlighted in this blog post.
Most users will not have to do anything to continue receiving webhooks. Users with services behind firewalls might want to double check whether their firewall rules include the full list of addresses. The full list of Atlassian IP ranges can be found here: https://ip-ranges.atlassian.com/
As always, please contact our support team if you have further questions or if you need further assistance.