<edit> Solved by Slate Digital; they provided a new 'B' installer (maybe I missed that one somewhere along the line)  
 
...I can insert Slate FG-X on a new project and save and reopen successfully.
 
On some projects I'm told the iLok driver is not loaded (which it is, and the service is running and I am on the most recent iLok driver). I also cannot insert the plug anywhere on these old projects either. 
 
Sometimes this happens for Slate Trigger2 as well, but not always.
 
This failure only seems to happen on projects that were started and saved with CbB. Any project that was started and saved in SPlat seem to be ok.
 
I'm thinking that it must have been in one of the earlier releases of CbB that dinked up these projects, because as I said I can start and save a new CbB in 2018.09 with FG-X and the project will reload properly. 
 
How to fix this?

BTW, never had or have this problem in Reaper, Mixbus (since V4) and Studio One Pro (V3 or V4).

Reboot?

Wibbles
Reboot?

Same.

This isn't going to be the best because you have to know your plug settings used, but maybe load the offending old project in safe mode without permitting slate plugs from loading the same it as songname-noslate.cwp Then load that song in normal mode and reinsert FG if possible?

This might be related to the iLok cloud feature.

bitman
This isn't going to be the best because you have to know your plug settings used, but maybe load the offending old project in safe mode without permitting slate plugs from loading the same it as songname-noslate.cwp Then load that song in normal mode and reinsert FG if possible?

I will give that a try.

Hidden_Symmetry
This might be related to the iLok cloud feature.

But would that not affect *all* projects?

FWIW my DAW is online 24/7 and AFIK I'm not using the iLok cloud. I authorize all my iLok software to my iLok2.

Did the windows 10 update go through on your machine? - this happens a lot with Windows updates. I know with every major Windows update...I have to fix my Steinberg Padshop synth...haven't had any trouble with Cake or Wave's licenses...I think sometimes AD2 I have had to fix the license.

This would likely be a 3rd party issue rather than a CbB problem. Have you contacted the vendor to report it?