I only found out last night that water makes the material crumbly (literally like the crumble on apple crumble).

I don't think that the issue is actually primarily the concrete weakening when exposed to water -- which does apparently happen -- but rather that the rebar internal to the concrete rusts.

You'll notice that nobody is complaining about "AAC" -- aerated autoclaved concrete -- but specifically reinforced aerated autoclaved concrete. The difference is the use of the rebar.

Granted, RAAC is probably used in places where structural strength is more important -- I don't know if a non-reinforced wall crumbling is as bad as a ceiling that's above someone's head.

The speaker in the video highlighted a new angle that I haven't seen before that I think is notable -- that specifically with RAAC, it's hard to tell if the rebar has been suffering from rust internally, because it apparently doesn't split the way regular reinforced concrete does.

Combine that with the fact that RAAC is particularly prone to rust damage to the rebar, and you've got a situation that theoretically shouldn't come up if the substance is protected from water, but if it does happen is prone to problems, is hard to diagnose, and has a catastrophic failure mode.