@IKD @Billldg
What looks like an oil film is actually extremely finely divided, poorly soluble or insoluble inorganic material. These are insoluble components of natural salts. This is something that we are able to reproduce in the lab, if we mix the salt to very high concentrations. It is also something that has always shown up, from time to time, in ours, and many other salts as well. It is likely noticed more often now, as people are looking much more carefully at their salt mixing solutions. You will often even see this “film” show up on the surface of the water in your spaghetti pot if you tend to add enough salt to the boiling water and you look carefully enough. This “film” is completely normal, does not affect anything, and is nothing to be concerned about.
I hope this adequately answers the question.