Going over the list: I'd limit 'errata' to math calculation errors (CR not matching Prof. bonus is excluded), the XP variance, and the missing DC on Cloud Giant.
Basing the proficiency on the CR is not a hard rule. I wouldn't include the 'errors' that refer to background math or general rules (large creature do double).
The formatting, spelling, and redundant 'damage' entries I'd correct in the next printing but not include in the player facing Errata.
For AL play, I'd consider changing CR values on the Giant Poisonous Snake and the Pixie - depending on how common the 'Pixiemancer' and 'Beastmaster with King Cobra' builds are in AL play.
Short List:
Change the resistance to weapon damage types wording to apply to all attacks - not just weapons.
HP
Horned Devil 178 (17d10 + 55) 148 (17d10 + 55)
XP for CR
Ancient Black Dragon 27,500 33,000
Ancient Blue Dragon 32,500 50,000
Ancient Green Dragon 30,000 41,000
Ancient Red Dragon 36,500 62,000
Ancient White Dragon 24,500 25,000
Ancient Brass Dragon 24,500 25,000
Ancient Bronze Dragon 30,000 41,000
Ancient Copper Dragon 27,500 33,000
Ancient Gold Dragon 36,500 62,000
Ancient Silver Dragon 32,500 50,000
Empyrean 32,500 50,000
Adult Brass Dragon Breath Weapons (Fire Breath) 49 (13d6) 45 (13d6)
Ankheg Bite 9 (2d6 + 3) 10 (2d6 + 3)
Missing DC
Cloud Giant -- 15