Since windows upgrade, SimpleLink windows app may have some issue with WhatsApp app (not WhatsApp web) or some other independent video calling / phone calling apps not opened in web browsers.
In this case, please click the app setting button at the bottom left of the interface, turn on TUN mode, and then following the indication: disconnect, close, and reopen SimpleLink, select the server and try again.
If still not working well, please contact customer support.