@F89, If you can't help this plant/branch, git it outta there ! Use snips and cut if off at the base. Inspect the cut on both ends. What do you see ? Look for bugs and their dodo, or any browning inside the stem.  It  sucks but that's what needs to happen. Unfortunately, if it's a root prob, it will probably take the whole plant, sooner or later. Time will tell. Think positive !! Happy growin