This is most common when there's a problem with the whitelist. In brief, whatever way you're accessing the Hub is not the way the Qlik Sense Server was initially setup. For example, by default when I install Qlik Sense to one of my VMs it will install to servername.domain.local (i.e. qliksense.domain.local). If I wanted to access the Hub via https://IP/hub then I would need to whitelist the IP. When you click on the QMC link on the server, what URL is used. What is the URL that is giving you that Engine error?