I have done extensive tests in vanilla, no mods, rescource or data packs were used during my tests. I have tested in the latest snapshot and also tested on versions; 1.16.1, 1.16, 1.15.2, 1.15.1, 1.15, 1.14.4, 1.14.3, 1.14.2, 1.14.1 and 1.14. This issue does not occur in 1.13.2 and thus I ended my testing there.

To re-create the issue, simply create a new creative world, make an End portal and insert all but one of the eyes of ender, then get an 8 minute ivisibility potion, a pickaxe and turn the gamemode to survival, place the last eye of ender and drink the potion (or the other way around, results are the same) then, making sure to not hold anything in your hands, enter the End dimention.

If you spawn on an obsidian platform, stand still and wait, the dragon will attack within a few mintues. If you spawn inside an endstone box, mine to the surface, making sure not to be seen holding anything in your hands by the dragon, once on the surface, stand still and wait, again, the dragon will attack within mintues.