Keep in mind that this may be the only form of nutrition the 'beta testers' are getting, and possibly have been getting, for a significant amount of time.

If you're eating normal food then some deficiency in one component of one meal may be masked by a surplus in another, and in particular if you eat a varied diet then that deficiency could start and stop within one meal. If instead your sole source of nutrition is suddenly deficient, it's not a stretch to think that you could notice a difference within 10 days.

I'm not trying to defend the product, I just don't think it's inconceivable that 10 days is long enough to notice a big problem with a formulation change.