AI Orion’s Spell bug - it was first reported here I believe (2.0 Known Issues - #541 by Onizakkii).
Today fighting against my defense team to test it out (on adroid), I also observed Orion’s spell failing to deliver damage to the last troop (it happend several times in different battles. Only when there’s a single troop left). The attached pic shows the moment right after Orion had cast his spell (sorry that’s not a video).