Why is this recipe cloudy?

[Paddington]

I have brewed about 50 AG brews across a wide range of styles, UK, US and European. I use Protofloc but no other fining agents. I always end up with very clear beer except a slight haze with heavily dry hopped beers and wheat beers (as you'd expect). However, I've had two goes at a dark bitter (Ruddles County-ish) and both times it has come out very cloudy.

The recipe is:
Maris Otter 5.5 kg
Medium Crystal 500g
Chocolate Malt 50g

Moderate UK hops at boil, 15 mins and aroma steep for 30 mins.

WLP002.

Ferment at about 20 - 22C for two weeks then bottle condition for three more.

It tastes OK and I'm not too bothered what it looks like but I just don't get why this is my one and only murky beer.

[HTH1975]

I can’t offer any explanations - nothing in the recipe to suggest there would be a clarity issue.

I’ve used Brausol for the last few brews and wish I’d known about it from the start. It also gets rid of chill haze.

Try it - I think it’s only about 7ml per 20’ish litre batch.

[Robwalkeragain]

Do you use the same yeast in other brews with no haze issues? The first place I would probably look is the crystal changing mash pH, if you don't regularly brew with a large percentage of crystal and your other recipes seem fine. That can go on to affect protofloc action, but shouldn't matter if you get a decent hot break. Also maybe look at how much starch you're pulling into the boil and what your overall mash separation is like.
Worth figuring out if it's a protein haze, if you have some caustic on hand just put a blob in a small sample and it should clear within a day.