Loot is bugged. Level 80 boss just dropped nothing, not even Atlas points.

Like, I don't understand how this is possible with 200% rarity and 60% quantity, plus a couple boss Atlas points.

I think the loot is bugged in some way, the final rare in a map is not dropping their guaranteed map, either.

I had that happening too earlier, the map was riverside if I remember correctly.
Same as you, neither the last rare nor the boss did drop a waystone, agreed on the fact it has to be a bug.

This probably needs to be moved to bug reports.