You are welcome
In my experience, it is really a thing. But I don`t know if it is just me? I am not talking about what is referred to as soda ash, but a super thin, invisible and slightly waxy layer I can`t really see. I get soda ash too, if I soap a bit cool and unmolds the soap a bit to early (I use mostly single cavity soap molds as I generously decorate the top of my soaps)
My recipe is with 60% lard. I use a 4% lye discount for the CPSR soaps (my safety asessor told me they don`t allow less than a 4%), but in my personal soaps (I make those just for our family) I always use a 3% lye discount. Still happens. But really, I am not bothered with it, it is mostly gone by the first 1-2 washes (depending on how much you rub the soap when a new one is started)
It really is a thing. I like soaps more on the 3rd to 4th wash than the first couple. I tell everyone the same thing.