No bug here, just some less intuitive mechanics.
Here's how the logic in the combat script runs:
Luria Nova is the region owner. They get to be the primary defenders.
Asylon is their ally. They're also on the defending side.
D'Hara is also there, but they're not at war with all the defenders (peace with Asylon), so they don't attack.
Barca is also there, but they're not at war with all the defenders (peace with Asylon), so they don't attack.
Thus, no battle.
This kind of counterintuitive situation will be clarified when I rewrite the combat script in a few months (at the end of the War Improvements Package).