The Google Chrome Team identified an issue with certificates created by Symantec and its other brands (GeoTrust, RapidSSL, Thawte). They mis-issued certain TLS server certificates. So all certificates have to be renewed accordingly.
You see this warning in your browser debug console as our CDN hosted player is distributed via Akamai, which is affected by this issue. Akamai is already aware of it, and in close contact with Symantec and Google and already prepared everything to update their certificates. At the latest until End of May 2018 all affected certificates will be updated and this warning should be no longer thrown in the debug console.
More details about this issue and actions to resolve it are available here: