"Unable to display page" with Oracle 12c Enterprise Manager Database Express
Try browsing to
https://[IP-address]/em  

For me this works, but everything is -very- -very- slow (a few minutes just to load the login page).

I'm suspecting the slowness has something to do with the certificate. Why the IP-address works and the hostname doesn't... probably some configuration issue.  

At least now anyone with more experience has something to go on...

For reference, all these posts seem to be about the same issue to me, but so far none has been answered:  


Unable to open/connect to Oracle 12c Enterprise Manager Express
Start Oracle 12c enterprise manager in Windows 7
How to run ORACLE 12C EM?
Oracle 12c Express Enterprise Manager on Centos 6.5 is not reachable