I place down my frenzy totem, and if my friend is on the same map and anywhere on the map, the frenzy totem tethers to him instead of me. I still receive the frenzy buff but not the tether buff, so if I play with my friend, the tether effect does not work for me. In the two images, the DPS with my friend on the same map is 1267 DPS; without my friend, it is 1912 DPS.
Yeah, same I have a temp fix where if the issue occurs, exit to character selection, and your friend should leave the area and then reenter together and hopefully, it fixes itself.