VMware Site Recovery Manager 8.x
This issue happens when there is an expired certificate in the environment (machine SSL certificate for vCenter, SRM, etc.). Issues can also happen if the certificates are recently renewed.
Refer document to change SRM appliance certificate - Change the Site Recovery Manager Appliance Certificate
Refer to the document to reconfigure SRM - Reconfigure the Site Recovery Manager Appliance.
Perform reconnect of Site Pair post reconfiguring SRM's, refer - Reconfigure the Connection Between Sites.