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The pilot tone serves the function in the receiver of restoring the carrier to the double sideband suppressed carrier L-R signal so it can be demodulated. The 19 kHz is doubled to 38 kHz and the phase is important as well as accurate frequency.
Joe, this is a wild speculation but it is well known that some Chinese components are “knock offs” which have been reverse engineered and are of substandard quality. Is the chip you substituted a genuine Rohm part? Maybe a bad run of chips was used by the manufacturer.