I had something similar happen a few months ago flying from SFO to ORD - wife (no status) in the window seat, baby as a lap infant, and myself (AA Gold) in the aisle seat on the same PNR and the AA app would show the middle seat as occupied. I tried changing seats to a row where all three seats were empty, and the “occupied” middle seat would follow me around. Then I decided to check EF and it showed that the middle seat was indeed blocked, so it seemed like a courtesy block for a lap infant to me. Didn’t bother calling AA but our flight went out with the middle seat empty which was nice.