It's clear that Shangri-La worked initially but then, contrary to all theory, it just mysteriously stopped working.

Frankly, I'm surprised that this "Shangri-La" approach is taken seriously by you and other people here on LW. I do believe that it has worked for many people, but this looks exactly like the sort of problem where placebo should be very effective on average. On the other hand, Roberts's theories about it don't even sound like a good just-so story.