There are lots of things it could be. I'm thinking it may be dead algae. One thing I learned here is to keep it at shock level until all 3 of these conditions are met:
- the water is crystal clear (you have a checkmark on this one)
- the free chlorine (FC) does not drop by more than 1 ppm overnight. This must be tested around dusk and then dawn because UV from the sun will cause FC loss.
- the combined chlorine (CC) is less than 0.5

And then, shock one more day just to be sure

If you already meet these criteria, then the cloudiness is caused by something that's not organic and isn't oxidizing.