The aquarium stood for ~12 years without any issues, and the failure occurred just months after reopening from years of "modernization". My first guess is that engineering changes or updates made then were somehow related. The acrylic was apparently designed correctly at least to the extent that it lasted through more than a decade of use before "modernization" whatever that means.
I also heard a theory that freezing temps might be related which would only be plausible if the atrium wasn't consistently heated. Temp can in theory affect the strength of acrylic bonds.