Knight Color Fail / by Chaotic Colors

Okay, so we all know that Chaos is fragile, but I would like to know a little more about what went wrong here to prevent a similar situation.
So please share any knowledge / advice you might have on the matter ;)

My process on the armor plates:
1. Base coat black (Vallejo primer)
2. Electric Blue (Vallejo)
3. Gloss Varnish (Vallejo)
4. Black wash (Vallejo)
Client then decided to change the color of the army to white.
5. Celestra Grey (Citadel)
6. The paint then begin to peal off, and I decided to wash it off with a small soft toothbrush.

The obvious would be to blame the wash underneath, for interacting with the Celestra Grey?
And maybe this could have been prevented with a layer of varnish, before applying the grey? 

Any help will be much appreciated  :)

Embrace the Chaos
Chaotic Colors