In 1.14.4, I have not come across this issue, but in 1.15.2, sometimes, when falling down from a height from which you should take fall damage, no fall damage is taken. The "fall" sound effect will play, but not damage is done to the player, similarly to what would happen if the gamerule fallDamage is false.

This issue can be seen in this video https://www.youtube.com/watch?v=C6SZtcoeCu0 at 12:49. Even though it might seem like the elytra should have prevented all fall damage, a small amount of damage should have been done, considering the velocity and angle of the player. This is confirmed by the fall damage sound, but no damage is done.