Sometimes when the dragon shoots fireballs at you they can collide with the dragon itself, making area effect clouds randomly appearing floating in the air. After trying many times seems that this doesn't occur in 1.16.5.
You can experience this in a normal dragon fight, however the chances are random.
@unknown, did you by any chance add 1.16.5 as affected by mistake? because i can't seem to reproduce this in that version.