Reduced volume playing aac files on Play1s

AAC/M4A files play at near-inaudible volume on a Play:1 stereo pair running software 17.2.7 (build 861080260). Same files play normally on current-firmware speakers (One SL, Era 100, both 18.8) in the same system, and FLAC is unaffected on all speaker. Confirmed same-controller, same-file, only-destination-differs test. Confirmed with multiple aac files - all play at usual volume on later model speaker and almost inaudible on my Play 1 stereo pair. I suspect this started after the latest OS update. Anyone else experiencing this??