I have 2 computers with Sonar installed. One is a work PC and the other is strictly studio.
 
I installed Addictive Keys last night on my work computer, no problems. Works like a champ. A little while ago I run the latest updates on Sonar, install a few plugins along with Addictive Keys on the studio machine. Everything is fine except no Addictive Keys anywhere. I have scanned for VST's several times and see AK being scanned each time, no errors, but it's nowhere to be found in Sonar. I've un/reinstalled twice. The dll is in the vst folder right under Addictive Drums that is listed in Sonar instruments
 
Any ideas what is going on?

I have Sonar Platinum and latest update installed(2017.01) and i find my copy of Addictive keys over there:
 

No such luck here...

Go to XLN website, de-register that computer for AD Keys and then re-register it again and re-install AD Keys.

Does 'nowhere to be found' mean it's not listed in Plugin Manager under VSTi? If it's there, but not listed in the insert menu, have you checked the 'Uncategorized' section? I don't recall if Addictive Key was picked up automatically as a Piano though you might expect it would be. And, of course, if you're using a custom plugin layout you might need to add it.

On my work machine, it's listed under piano. On the other one it's not listed anywhere at all.
 
When I manually scan for new vst's I can see it specifically scanning Addictive keys, but it doesn't appear anywhere in the list. If I use the search function the only thing it finds is addictive drums.
 
The scan results are the same if I install or uninstall AK. 133 found (123 New 0 errors 0 removed) But when installed it DOES scan the dll.

Listed under Piano for me also.

Try to write Addictive Keys Standalone to Windows search and start standalone program and see what happens.

The standalone works like a champ. It's just really strange.

Try doing a VST RESET followed by a RESCAN