Guild Wars 2

Ranger elite skill Spirit of Nature can’t revive players and NPCs, because when you use Nature’s Renewal with traited Spirits Unbound XI , and start moving, spirit will just stop doing its animation, and follow you around, canceling its action. This will set skill on cooldown, but there won’t be any effect.

This usually happens when in big group of players.

Yes, this is so very annoying in PvP when its crucial to get the res and all of a sudden the spirit becomes completely useless.