Good advice, thank youDon't stress over it. There are a zillion ways to raise chickens and there is more than one right way to do things.
I and others I know, use ACV in the water all the time, even when it is hotter than hell because it keeps the waterers cleaner, and we haven't had problems with chicken health, or with thin shelled eggs. Some others may have had problems, but you know, there are so many variables that go into each situation, that you usually will not know if that one thing was the cause of a problem or not.
I will say that my chickens are fed a free-choice high protein diet marketed as a "game chick starter" because that is what I have researched and felt is best for our flock. We also have free-choice oyster shell available as a calcium supplement. I've dropped eggs from chest height onto the ground and not had them break and have difficulty candling them because they are so thick. So perhaps how we feed our chickens overcomes the issue that is currently being discussed about thin shelled eggs.
Don't try to make this too hard. If you like the benefits of ACV, try it and see what happens. If you wind up with something odd and you think the ACV might be the problem, stop the ACV and see if the problem resolves for you. Chickens are tougher than you think and you can experiment with most things to get your husbandry skills down pat without too much risk of killing them. And there is more than one right way to raise chickens.