Unfinished Business Done but Not complete.

Bioware made this game, not EA. 😉 It's also not a very common issue, hence why it wasn't given priority during the time when patches were still being made for this game. (No further patches are intended for this game).

If you got the approval point gains for killing each target, I don't think there's actually anything else to be gained when the quest triggers as completed. Sure, it might be annoying that it's still in your journal, but you're not missing out on anything. You can still do any other Cassandra related quests.

Not sure with this one, but sometimes after these sorts of quests, you need to speak to the quest giver again for it to trigger as completed. Doesn't hurt to try, at least.

This game was built on a completely different engine to the previous games in the series, and thus far I don't think anyone's had any success with console commands, so I doubt you're going to find a fix that way, sorry. There is a save editor, but I don't think it has anything in it about this quest.

So, sorry I couldn't provide better news. You can try repairing the game (right click it in Origin and select 'repair game'), not sure if that will help at all, though. Or try loading a save before you killed the last target, and see if that will trigger the quest as completed when you kill the target again (I had to do that with this quest in my most recent playthrough, with the target in the Emerald Graves). Otherwise, you're just going to have to put up with this being stuck in your journal.