Does distracting, as in for the help action, drop invisibility (from the distracter)?
That depends entirely on what you say your character is actually doing with the Help action. It's
much easier to distract someone when they can see you, so a lot of the normal choices just won't work. You can't feint an attack or pretend you're doing something really threatening. Is he making a lot of noise similar to what
minor illusion creates? That might not even work and might not count as the Help action at all. Are you opening your purse and emptying it on the ground? If the creature is greedy, gold appearing from nowhere might distract him! Are you using your staff to try to trip the creature, or grabbing at him, or pushing at him? That could be an attack. How exactly was your character trying to distract the opponent?
If you just say, "I use the Help action," then the DM is pretty free to interpret Help as he chooses. If his interpretation is that your character does something that makes you visible, well, you're visible. That's why you're supposed to describe what you're doing.
No it isn't.
As others have said, the DM in AL is perfectly free to rule how he wants if there is disagreement about the rules. It does not matter if the table disagrees with the rules or if the rules disagree with each other. The DM is always the final referee. That doesn't mean an AL DM can do anything he wants. WotC typically requires AL DMs to include and use as much material as possible, doesn't want them to use homebrew material or significantly modified adventures, and uses the PHB + 1 rule to limit character complexity. But the DM is still the DM.
As far as for
what Crawford has said about attacks: "An attack involves an attack roll or doing something that the rules call an attack, like grappling or shoving." Personally, I don't put much stock in Crawford's answers because they often seem to result in very unrealistic results. I only use them when I don't know how to rule.
Oh, and PHB 195 says you can only make opportunity attacks against opponents you can see.