Reproduction:
On the server provided by Aternos. I am on 1.14 Prerelease 5. 4 players (including me) have joined this server before.
I respawn the dragon twice (it may be visible on first dragon though.)
I destroy all the ender crystals. I kill all ender crystals to make sure that they do not affect the AI of the dragon. They still appear to have glitchy beams leading to the dragon, although there are no ender crystals.
Result: Dragon flies between three pillars.
Video of the glitch is in link because it exceeds 10.00MB.
Please check if that's still an issue for you in the latest 1.14.4 stable release or the latest 1.15 development snapshot.