I think to the extent that there would be post-AGI sub-optimal decision making (or catastrophe), that would be basically a failure of alignment (i.e. the alignment problem would not in actual fact have been solved!). More concretely, there are many things that need aligning beyond single human : single AGI, the most difficult being multi-human : multi-AGI, but there is also alignment needed at every relevant step in the human decision making chain.
I think to the extent that there would be post-AGI sub-optimal decision making (or catastrophe), that would be basically a failure of alignment (i.e. the alignment problem would not in actual fact have been solved!). More concretely, there are many things that need aligning beyond single human : single AGI, the most difficult being multi-human : multi-AGI, but there is also alignment needed at every relevant step in the human decision making chain.