ADFS Self-Signed Certificates are used for internal encryption and are separate from your SSL certificates. You can sometimes experience a situation where these internal certificates auto-rollover. when this happens it will bring CRM down.
Below is a blog that has a fix for this that seems to work if you follow all the steps to a T:
Additionally there is a way to push the date out using Powershell to make the renewal duration more like 5 years instead of every 365 days.
- Happy Tuesday!