Thank you for your question. While I haven't heard of any issues specifically for the wifi on American Airlines it is possible that their wifi has its own filter in place that may conflict with our own. I do have a couple of suggestions to try to get through that wifi portal.
First, try restarting your phone. As soon as it is up and usable try connecting to the airplane wifi. Second, if feasible, try disabling the filtering on your account temporarily and then refresh the Covenant Eyes app on your phone. Doing so should remove any potential filtering conflicts.
I hope you find these suggestions helpful and I do apologize about the hassle. Thank you and have a great day.