I've screwed around with this for hours/days now.
Adobe tech support tells me it is the plug-in sponsors' responsibility to have their products work with LR CC. Plug-ins cos. (NIK, TOPAZ OnONe, etc.) give convoluted work-arounds, that don't work.
A friend just told me that he download LR CC from Adobe Photography subscription and all his plug-ins now work.
Do I have to uninstall LR CC and Photoshop CC and reinstall?
Will this fix the problem?
I have seen some reports suggesting that the plug-ins need to be updated.
For the NIK plug-ins, go to their install directories and run each EXE. This may jumpstart their update code.
I just figured it out! I opened LR CC - went to File -> Plug-n Manager -> Check for Updates -> Install. When I did that, everything showed up.