First, let's try to understand what is being skipped. As the message says, is strafe phase. What is that?
The official minecraft wiki says:
Strafing - the dragon will fly towards the target player. When it is
within 64 blocks, it will fire Ender charges and resume circling. If a
players destroys an End Crystal, the dragon will immediately switch to
this state to fire an Ender Charge at them.
While the question lacks a detailed log, with the information provided I can think of the following outcomes:
- The player destroyed the End Crystals when the Ender Dragon was at 64+ blocks of distance. The wiki mentions that the strafe happens when its within 64 blocks
- The player destroyed the End Crystals AFTER the Ender Dragon was killed, so the dragon position is empty (because its dead) so its not within 64 blocks either
- The player cheated somehow and made it so the Ender Dragon could not detect him as a player, which would also cause a "fail to strafe" message
This is the only things I can consider that caused the message.