To be clear, I was not advocating that the salt be added last, or later in the process. I was only trying to make the point that salt can be made to dissolve in a dough when added later. For Saul's situation, I would do as pizzanapoletana recommends, as discussed at length earlier in this thread. I would also advocate reviewing the sequencing of ingredients, also as previously discussed, and for the reasons previously discussed.
It is possible that if the amount of yeast currently being used is on the low side, the relatively large amount of salt may be impeding the fermentation of the dough, as pieguy postulates. Salt does indeed act as a regulator of the fermentation process and it is quite common in Naples to use it as such--by increasing it (to slow down fermentation) or decreasing it (to speed up fermentation) as the situation demands. I might add, however, that 2.75% salt for a Neapolitan dough is well within the range usually used. It might be too much in relation to the yeast, but it, per se, is not out of line. I have seen over 3%.
A knead time of 20 minutes would not be out of order for a 00 dough that uses 00 flour on the low end of the protein/gluten spectrum. The mixers in Italy are different from what are used in the U.S., and possibly in the UK, but low protein/gluten doughs require long times to develop what little gluten is in the dough. This is a point that pizzanapoletana has made on more than one occasion.
The reason I quoted the Lehmann posts was to point out the more common causes for bubbles forming. The reasons for bubbles forming in a crust are essentially the same as why they form in a dough before baking. Tom Lehmann mentioned underfermentation and low yeast as two of the possibilities. With the low dough temperatures that Saul has reported achieving with his dough balls, and especially if the yeast is in fact on the low side, suggests underfermentation to me rather than overfermentation.
I think Saul has now been subjected to much discourse on which to evaluate what he is doing. I like trying to resolve dough mysteries and look forward to his informing us on the progress he makes in unraveling this one.