What is a normal quiescent current in BJT class AB amplifier
I am not really an audio guy. But I took a look at Douglas Self's "Audio Power Amplifier Design Handbook." Those values, of 55 to 59 mV are ballpark. You might want to warm up the amp (by playing some music) and then check it again when it is warm.

As far as the mismatch goes, it isn't a huge mismatch. But were you measuring it with a load attached or no load? With no load, the two resistors are perfectly in series (or so I assume), so the currents have to be the same. In that case, any voltage mismatch is due to Re mismatch. You can tune Re by adding resistors in parallel with whichever one is higher in voltage until the two voltages match each other. Again, do this with no load attached to the amplifier.

If the two Re's are already matched, but you have different voltages across them when a load is attached, that is due to an output voltage offset. Unless it is large, I wouldn't worry about it.

Ultimately, bias current should be set based on what produces minimum distortion, not on anything else. But it is not very practical for most people to measure distortion while tuning bias current.

Good luck!