Sour can be low brew temp. Can you run some hot water from the head of the Auto before you run the shot to warm it up a bit this might lose some of the sour?
That lighter colour will be more Bitter and is over extraction and blonding by the sounds of it and this might be helped by a little finer grind or even stop the shot as soon as you see it.
To help you identify what you are tasting pour the shot into 3 glasses and drink them seperately is worthwhile to help in identifying what you think you are tasting.
Beans also play a big part as does the machine which is part of the reason Autos are evil

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