Where's the downspout? On the other end of the run? I'd say it's most likely an issue of not having enough downspouts. The gutter fills up quickly from roof runoff and if there aren't an adequate number of downspouts to drain the gutter you get overflow like that. incorrect sloping can add to the problem. If the gutter slopes downward to that dead end it will just start overflowing there first.
Also, can't see the layout of the roof, but could the roof possibly be funneling water to that far edge of the gutter so that it's not being properly captured by the gutter?
Also, can't see the layout of the roof, but could the roof possibly be funneling water to that far edge of the gutter so that it's not being properly captured by the gutter?