When adding a new Node Manager to your Spotfire environment, the initial trust of the Node Manager is successful but after a few minutes, it shows it is offline. On the Node Manager machine, look at the nm.log file. You may see the following:
INFO 2017-11-03T21:35:41,224-0500 [] nodemanager.trust.DelayUntilAuthorizedGate: Unable to use certificate to contact the server at Node [serverId=00000000-0000-0000-0000-000000000000, serverName=tss1.tibco.com, port=9443, online=true, siteID=00000000-0000-0000-0000-000000000000] on port 9443: I/O error on POST request for "https://tss1.tibco.com:9443/spotfire/nodemanager/messages": sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: Response is unreliable: its validity interval is out-of-date; nested exception is javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: Response is unreliable: its validity interval is out-of-date