First, try printing the BP. If the Pre-Check symbol appears on the paper BP, this has to do with your mobile BP, you will have an answer and can resolve that later.
Second, double check that the name in your AA profile matches the name under your KTN exactly (down to extra punctuation and spaces). Reportedly, TSA and air carrier matches are better/tougher and if there is a mis-match that means no Pre-Check.
Third, remove your KTN and re-enter it. Or call AA and have them do it for you. Log out and then log back in. See if Pre-Check reappears.
Fourth, try again at the airport.
Fifth, as others note, Pre-Check does have random de-selection and it's just not your day. The purpose of the symbol is to give you time to allow for going through the regular line. I've had 100% success with GE as have most people I know, so it's just your unlucky day if you get to this point.