I don't ever recall seeing the Stagioni flours in the U.S., but I am aware that there are several 5 Stagioni 00 flours. Do you know which one you are using, that is, Oro, Superiore or Rinforzato?
There is a spirited debate on the forum about the salt/yeast issue. However, one of our members, pizzanapoletana, who comes from the Naples area (he now lives in the UK), has had a great deal of experience in making Neapolitan doughs and insists that it is fine to combine salt with the yeast in the water provided the salt is completely dissolved in the water before adding the yeast (preferment or commercial yeast). I have excerpted the following from one of pizzanapoletana's posts in which he discussed the salt/water issue:
I keep hearing that salt and yeast cannot be combined in the water before adding the flour.
Before saying that, people should consider what actually the salt does to the yeast.
Basically, salt excerpt [exerts?] what is called osmotic pressure, which means that attract the water present in the environment around it. Sugar has a similar effect, even if at a lesser extent.
At the same time, the osmotic pressure, slows down the action of yeast in a dough.
We should also consider that different salt types, have different hydroscopic properties (the capacity of be dissolved in water), with the sea salt being the best.
Now, if you dissolve the salt in the water, and then into this "brine", dissolve the yeast (like Neapolitan have been doing for ages) the Osmotic pressure will be the same as if you add the two separate, as well as the salt will be already dissolved and have absorbed enough water, which will have reduced its osmotic pressure.
The only other thing to consider, would be the effect of salt on the formation of gluten, but this is another story.
Can you tell me what kind or brand of yeast you are using? I assume that you are using what we in the U.S. call either "active dry yeast" or "instant dry yeast", both of which are dry forms of yeast. The active dry yeast has to be proofed (activated) in warm water before using. The instant dry yeast can be added directly to the flour. I mention the yeast in light of your comments about seeing specks in the water. It's possible that the form of yeast you are using may not have been properly handled.
I do think that you may want to take a careful look at the sequencing of the ingredients, along the lines mentioned earlier. BTW, the 75 degree dough temperature may be a bit on the cool side but if the dough is permitted to warm up enough before using, it should handle properly. How long do you allow the dough to warm up when it comes out of the cooler?