The Bug
The Ender Dragon only stops on the End Portal for ~5 seconds, not really letting any player get a hit on her before she flies away again. This means that the dragon fight is more tedious and mostly waiting for those without arrows. This bug did not occur in 20w18a.
Here are five gifs showing how quickly how the dragon flies away after landing:
https://gyazo.com/83b060e7e263cc284f8c3a69c655ee63
https://gyazo.com/c59f50513259721d18c104e28b0742dc
https://gyazo.com/79e226f93c1d6d7ea3cb8e56f9539f6e
https://gyazo.com/cb6ee2625c4fda9159a594ab3339b775
https://gyazo.com/17cbbbb0edb5a4c31580cddd82c5845e
These aren't cherry picked instances, it happens every time.
Fixed in 20w21a.