very very confused?????

ok so i was fighting these two guys and they kept killing me again and again but for some reason i couldnt damage one of them and im not sure if this is exploiting or something but there were only certain times i would be able to damage the person. the only time they ever attacked me was when i was about to kill there teamate and then they just kill me and i cant do anything about it bc i cant damage them. i recorded it a bit but idk 😭