This bug is already known, sometimes you can also see opponents respawning, and disappearing just in the same second - they still attack you, but you don\'t see them until you are dead. Or other players kill the opponent you selected before you can attack, because they don\'t see you, or you don\'t see themand are surprised by the opponent falling down, or getting a message that you must be grouped.
The usual workaround is: \"/unstick\" once, carefully. Wait until you were moved. Then you may be lucky to reappear before the opponent attacking you has killed you.