If using action camera during victory or death, you cannot lock onto the 3 flying dragon minions (Ogravros the Moondeath, Fafnarin the Heartslayer, Horrogos the Soulbreaker) without exiting action camera mode. Due to the mechanics of the cannons, this means you are unable to attack them at all unless you realize that this is the cause of the targeting issues.
Like every other enemy in the game, they should be targeted by looking at them when in this mode. Alternatively, using 2 should just attack them automatically, as the cannons during the Zhaitan fight do, since they are the only legal targets anyway.