In brief, my idea for why Kant's Second Analogy (arguing for the law of causality) in the CPR seems so fucked up:

He conflates the first part of his argument (that there must be a rule in our understanding correlating the order of subjective apprehensions with the order of objective appearances) with the second part (that there must be a rule in our understanding giving a determinate link between any objective appearance and a preceding objective appearance).

Since I've spent the best part of a day ferreting out this flaw amidst his disorganised jargon, it'd better be one.