Are there any harmful effects of drinking too much apple cider vinegar?

Too much of anything: There are harmful effects of too much of anything! Even drinking too much water can kill you. And anything that helps can also cause harm. That said, apple cider vinegar is fairly safe but should always be diluted. It appears to be wise to limit consumption to 2 tbsp per day. See https://authoritynutrition.com/apple-cider-vinegar-side-effects/