Did you go through the full calibration procedure in the documentation for the sketch - because it sounds to me like a phase error in that c.t. It starts on page 6.
Over the years, the phase error of those c.t’s has changed as the manufacturing has changed - and I don’t have access to all those arriving in the shop to be able to test them. It’s certainly true that the early grey-lead ones have different phase errors to the black-lead ones.
