Hey @wc19888, 
This is just a warning (not an error) — it doesn’t break anything and the server works fine. You can safely ignore it for most deployments.
Try turning off validating certificate by Document Server. Set services.CoAuthoring.requestDefaults.rejectUnauthorized=false
in /etc/onlyoffice/documentserver/defaults.json file and restart documentserver serviceis with supervisorctl restart all .
rejectUnauthorized - Defines if the certificates will be verified by the Document Server or not.
Recent related thread with Admin Panel:
https://community.onlyoffice.com/t/cannot-access-admin-panel-of-the-documentserver/18609 