Finally discovered that the sector was glitched. The first time in, it was just one champion squatting on the chest. Got fed up and left. On my second run there were 2 barrier colussus champions. WTF? Came back later for a 3rd try. 2 champs sitting on my loot again. This time, however, there was a screen prompt to retrieve the cache. Snuck up the side path, ran to the chest and it opened. 2 champs despawned. So, killing the champs isn't necessary to compete the sector, but cache code prompt never proc'd on the first 2 runs and I killed everything but the ones at the chest. Such bullsh!t from this game sometimes.✌