Certificates need to be renewed for some customers on Lync. This is in order to continue to provide functionality for some of our legacy IP phone offerings (e.g. Polycom CX600).
If you are affected by this change, you will shortly receive an email from us. All that's needed is for a domain admin to be available to approve a new certificate request on Saturday 1st November. It should only be a case of monitoring emails, and clicking a link.
If you have any further queries, please raise a support ticket in the normal way.