Glasses appear to be clean. Drinking water at first tastes fine. Left to stand in the glass for 10 minutes and a strong sour taste dissolves into the water. Have tried reducing rinse aid but this doesn’t help. Using waitrose own detergent tablets and rinse aid.
If it appears to be functioning perfectly in all other aspects then the first thing I would try is a different detergent. Fairy Active Bursts give good results.