Well here's the thing
i played like 2 matches (1 with a friend and another random) using my monarch deck, they summoned blue eyes chaos max dragon (effect: cannot be targeted or destroyed by card effects).
I summoned erebus and did this effect: discard 2 monarch spell/trap cards and target 1 monster on the field and shuffle on the deck, i targeted blue eyes chaos max dragon and voila! chaos max dragon directly to deck from field.
my friend told me that's a bug e_e
i want to be 100% sure of this.

erebus effect does not target, it shuffles the card you choose (or random, if from hand) at resolution so chaos maxx's anti-targeting is irrelevant here