Please try the suggestions outlined above.
Also, are you on a Mac by chance? I’ve noticed some weirdness lately running / trying to run Start.jnlp and Admin.jnlp on my Mac, even after emptying the cache, etc. I’m not sure what the issue is myself… it might have to do with recent security updates and new anti-tracking / Private Addresses that Apple has implemented on recent versions of MacOS. —Things aren’t even consistent between two different macs when running the admin console and having downloaded them the same way. Really odd since Java is meant to run the same regardless of platform.
As soon as I booted into Bootcamp running Windows 10 on my Mac, everything worked as expected. Just something to try if you happen to be Mac based yet have access to a Windows machine.
(Spoke too soon... Windows had problems, too. Possibly a network communication issue. Still investigating.)
As far as controlling devices, I have found the new UD Mobile to be much more responsive than other apps that have worked with my ISY in the past, even though I am running them all solely on the local network. I can only guess that those other apps need to be updated for more recent releases of iOS for them to function as well.