I hate to be the bearer of bad news, but the Stormzilla / Stupendor-X battle is still bugged.
Stupendor-X's Riposte talent is mis-firing, reacting when the Stormzilla hits him instead of after a miss. (It pops up as a Riposte, but it's acting like a Vengeance Strike instead.) Of the two, Vengeance Strike is more useful - in the few battles I've done since the update, Stormzilla hits more often than she misses.
Could you please keep Stupendor-X's talent working as-is, but 'fix' the overhead display to correctly show it's a Vengeance Strike instead of a Riposte? Thanks!
Does the stormzilla have second chance? The order of things means that second chance activates before riposte, so what you may be seeing is the stormzilla miss, then hit with second chance, then Stupendor-X does riposte.