On Attack CTC works like on Striking CTC when using a Sequence skill. If the attack misses, the On Attack CTC will not play.
I gave myself a Pilum with 100% Nova on Attack and 100% Frozen Nova on Striking. Against a monster in which I have 5% chance to hit, using Normal Attack sees Nova every attack, though the miss indicator is there for 95% of my attacks. When the attack lands and there is no miss indicator, I see both novas. When using Jab, Nova is only there for 5% of my attacks, the same attacks that Frozen Nova goes off. This happens with Double Swing, Frenzy, and Act 5 Mercenary’s Normal Attack as well.
Edit: for clarification, this bug exists in LOD too. Who knows how long it’s been around.