Before version 1.14, the ender dragon would dive straight down to the portal, after, it descends while turning side to side in a obvious buggy matter. It seems to also remain at the same y value rather than fly around the pillars fluently. It seems to rarely ever descend to the portal to perch unless all crystals are destroyed, it previously did it very  frequently. It also no longer dives or strafes to fire a fireball, but rather flies above them in circles before firing it, and its divebomb attack is now missing as a result. This issue has already been reported, but it was marked invalid as the original report used mods, so pls dont mark this as a duplicate or invalid because this is vanilla and this is a game breaking bug. Some screenshots of before 1.14 and after: