Clearly she got an auto attack off on her 3rd passive while stunned by Sona R. Is this an auto attack bug of some sort? Does not seem intended at all, that auto attack cost us the game.
Was she even stunned? It looked more like she got several autos over such a short duration to the point where I doubt she was cc`d in the first place.
It kind of looks like she disappeared at one point mid R, when your ult was going to hit her... maybe she cant be hit while ulting?
She didn't AA during the Sona ult.
Her blade is glowing before she dives, which means her next AA will proc her passive. Sona ults her in the middle of her R, but still gets hit by Q/W from Diana, who then stands at Sona for the remaining duration of Sona's ult. A second after landing she manages to throw her first AA, as can be seen based on the fact that it procs her passive(AOE Damage around her.)
If she had auto'd during Sona's R, her passive wouldn't still be primed for that final AA that killed them.
(Also, her R damage was stopped by Sona's R, confirmed by the fact that Sona didn't die until a moment later when she was able to AA. You can CC Diana mid dive when she uses R, and stop the damage - But in many cases she'll still finish moving to her target/behind her target without dealing the damage.)
Side note - The horrible quality of this video makes it extremely hard to tell what is going on. I dunno if you slowed things down, or if you just play with 15 fps - But even as a many-year Diana 1-trick I had trouble seeing through it to pick out what happened.
