If the certificate which you have added as the token-signing certificate has been set to secondary, you need to change it to primary, as shown below.
1. Right-click on the Token-signing certificate and select Set as Primary.
AD FS management console
Certificates used for token-signing are critical to the stability of the Federation Service. Because loss or unplanned removal of any certificates configured for this purpose can disrupt service, you should back up any certificates configured for this purpose.