I encountered this issue in one survival world that after travelling to the End, there was one naturally generated crystal that I kept shooting with an arrow that did not break even though I hit and broke other crystals. 

I created a new 1.14.1 creative world and after travelling to the End the issue did not happen.  I regenerated the world and tried again and this time the issue happened again on 3 crystals, so the issue is intermittent.  

Characteristics of the crystals were:

• The crystals still healed the dragon
• The crystal will still explode if hit by a melee weapon
• Eggs thrown at the crystal hatched baby chickens but did not break it
• Arrows disappeared when hitting the crystal but didn't break it
• After saving and re-loading the world, the crystals were not present and only fire above a block of end stone was left (this is a possible workaround if the player is aware of it)