I've noticed this a few times now, mainly as mages. Basically if my team is focusing down someone, and they pop a shield (maybe Janna shield, or Barrier, big shields like that) and I autoattack them so it consumes part of the shield but none of their actual health bar, sometimes you don't get an assist when they die just afterward. Is this intentional or a strange bug I need to investigate further?
It's a bug.
It may be intentional; Assist are granted if you do damage (among other things ofc) to an enemy and there is a mechanic where if the damage is done to a shield it does not count as damage being done to the champion as that's defined as causing the lowering of health.
Damaging a shield doesn't actually count as damaging the champion in the games code. You'll notice that hitting someones shield during their recall won't stop the recall either. It's a stupid interaction but that's how it is. And you gotta do damage or buff an ally to get that assist.
