Ancestral Guidance, the Druid Paragon Legendary Node, has regained its old bug where it counts your resource costs AFTER discounts, instead of before, as it does on live.
This means high resource cost reduction or unlimited resources (Mjolnic Ryng) cause it to seldom or never activate.
This was an old bug with previous seasons, and was eliminated a few seasons back, but the horrible old code of the PTR has revived it.