"While in a Sanctuary, you cannot attack other players and other players cannot attack you." - But warden's ultimate bear pet can attack. Even more - players from the ground (not in Sanctuary) can attack warden's bear-pet that stand in Sanctuary.
This issue appeared on PC-EU server in Imperial City (CP) in Arboretum district on 23th April 2021 ~22:20-22:30 (UTC+3 Moscow Time).
My wife and ~5-6 Red players stand in Sanctuary on this balcony when red player's bear pet attack her. First screenshot.

I was here at that moment (not in Sanctuary, second Screenshot) and killed that bear-pet with my bow when I saw bear attacking my wife's character

It must be a bug.