There are a few reasons your oils can separate.False trace.
This happens when you're soaping at cool temps or in an overly ventilated or cold room and the soap seems to trace right away but then liquifies again if you keep stirring. Given that you stick blended it for a while, this seems like a remote possibility.Low saturated to unsaturated oil ratio.
While soaping at low ratios is entirely possible, as with Castile soap, these soaps are much more difficult to make and require a ton of stirring. In my own recipes, I like to shoot for a 40/60 sat/unsat ratio. Your recipe works out to 34/66, so that's not too bad.Problematic EOs or FOs.
Not the problem here.Soaping at too cool temps.
IMO, this is probably the issue... barring any miscalculations or incorrect measuring. I treat my beer soaps the same as my usual H2O soaps in that I don't freeze the liquids, all ingredients are at room temp, and I pour into a wooden log mold. The way you treated your recipe is the way I would treat my 100% milk soaps. Freezing the liquid and then pouring into individual plastic molds (these molds have no built-in insulation like wooden molds do) may have kept the soap solution from getting to gel phase and hindered the saponification process. Did you put your soap to bed wrapped in towels or blankets? If not, they would have had zero insulation.Too much lye.
As for the benefits of beer soap, I would say the best one is the rich, creamy lather. I always use beer in my shampoo bars for both the lather and the shine qualities that beer gives you. I can't say for certain that the lye process doesn't kill the shine-enhancing properties, but my hair is pretty darn shiny!
As for what kind of beer to use, I always use the cheap, gross stuff that I would never drink and often find left at my house after a party, lol. It's a great alternative to throwing it out. I've never really noticed enough of a difference between brands in the quality of the soap to really worry about this (all beers seem to make nice lathery soap), but there can be differences in the color and the heavier bodied beers do seem to make a richer lather.
Although, no one has ever left a Natty at my house, so I can't vouch for all the cheap, gross beers!