Unable to Respawn Enderdragon Using Crystals

Whenever I attempt to respawn the Enderdragon the crystals placed around the sides of the end gate do not trigger the summoning sequence.  I attempted to destroy the crystals and left the end so I could craft more only for the 4 crystals to reappear in my hot-bar once back in the Overworld. I have attempted to do this multiple times and have repeatedly encountered the same result: no dragon spawning and crystals reappearing in inventory after  exiting The End.