Lightroom 6 is acting like a trial and expecting a serial. I have the photography subscription. I have tried restarting etc etc etc....
Have you tried signing out of the desktop app and back in? Sign in, Sign out | Creative Cloud desktop app
Solution 2 may help as well: helpx.adobe.com/creative-cloud/kb/unknown-server-error-launching-cc.html
Connectivity steps: helpx.adobe.com/x-productkb/policy-pricing/activation-network-issues.html
Run the Cleaner Tool to uninstall, then reinstall: Use the CC Cleaner Tool to solve installation problems | CC, CS3-CS6
I got it resolved. It was very complicated and took nearly an hour with tech support to resolve. They did a great job walking me through it it was not simple.