Mostly @gregbenz’s customers 
He has written what may be the ultimate guide to troubleshooting CCX installations: Lumenzia Installation ← Please read through his guide, and report back if any/which of the steps were helpful.
The official Adobe guide is here: Find solutions for installation issues with Creative Cloud app extensions and plugins although it could use some updates about installing CCX files from outside the Marketplace.
Is your problem happening in Windows or macOS? I ask because we see it more often in Windows…
Finally, if you’re still having problems, you can follow the steps here: Allow offline development - #14 by Erin_Finnegan