Nearby players that can revive you
The last update included :Added a UI element that shows nearby players that can revive you within 50m when downed. I have found that in most cases this is not operating correctly. On many occasions ...
Forum Discussion
Yes, it happens sometimes. But they confirmed there is some bug with the distances reported and I guess this falls into this area (the game thinks the player is farther than he actually is and thus it's not displayed). I think it should be fixed in the upcoming patch, as far as I remember some developer's tweet.
