Fish – re-hydrate dried and salted cod with water and milk

Per this paper, you want an extraction time of 15-60 mins at 113F / 45C. This patent uses temperatures below 131F / 55C. Both of those temperatures may be too low to make the cod actually taste good / cooked. 140F is a fairly typical temperature for sous vide fish. While 113F has some interesting results, it may or may not work for your dish as the result comes out quite different than standard cooked fish. However, I don't think that using a higher heat will have a negative effect on the gelatin extraction, so I'd start with 140F and work down from there.

This process may cause other problems though. In addition to extracting the gelatin, any other juices from the fish will mix with your gelatin. In a pan, these may steam off, but with sous vide you're stuck with them. I think you're likely to end up with a mixture that's much more watery than if you used a pan. You may find that this needs to be boiled down a little bit in order to get the desired consistency of your emulsion.

As always with sous vide, you've also got potential safety issues. You'll never reach pasteurization at 113F. You should check Douglas Baldwin's A Practical Guide To Sous Vide for cooking times (which are highly dependent on width).

Assuming the cod was the same quality as before and you de-salted the fish in the fridge for 24 to 48 hours, then I would also guess overcooking. Rendering the gelatin at 45°C (as suggested in the paper @yossarian uncovered) should prevent the fish from cooking and give enough time to get it into the oil. You can always cook the fish in a separate step after you made the pil pil.

Modern techniques for salting cod use less salt and create a product that will not be edible by future archeologists, so store in a dry cool place (tightly wrapped in the fridge).