The only thing that went wrong with the Sundering was that Lahabrea, Elidibus and Emet-Selch were not Sundered (most likely). They are (as far as we know) the only beings who remember anything about life before the Sundering. All the major "problems" that happened as a result of the Sundering can be traced back to Lahabrea, Elidibus and Emet-Selch trying to get their own world back at the expense of all the life on the Source/Shards. All other life on the Source/Shard has no idea that the Ancients came before them and have no reason to even go messing around with the other Shards/Source since they would have no reason to know they exist. It's only with the Ascians meddling that we know other Shards existed and the other Shards started being destroyed which is what kicked off this entire plot.

I'd be very interested in knowing what problems can be traced back to the Sundering that have nothing to do with the Ascians meddling in the world order.

And I am very, very, very interested in learning how Lahbrea, Elidibus and Emet-Selch managed to escape being Sundered along with everything else.