Just tried upgrading from 4.7.3 following steps above. Cleared Java cache and opened the link http://isy.universal-devices.com/994i/5.0.16/admin.jnlp.
I saw the Java splash screen then NADA, Nothing. So as of now, I cannot access the Admin Console. I tried an ISY reboot & tried to open the Finder, but these did not help.
I asked Alexa to open a scene and that WORKED! I also checked the ISY portal and it WORKS as well. I can see v5.0.16, devices, programs and ELK status & find I can control devices. So it appears the system successfully upgraded with scenes and programs in tact, I just can't access the Console. I'll need to open a ticket to work through this issue.