We report about the fast Nova Sgr 2016 N.4 being surprisingly trapped in a long-lasting and bright plateau (Delta(I)>=10mag above quiescence), six years past the nova eruption. Very few other novae experience a similar occurring. We have carried out an intensive observing campaign collecting daily BVRI photometry, monthly high-resolution optical spectroscopy, and observed the nova in ultraviolet and X-rays with Swift at five distinct epochs. The bolometric luminosity radiated during the plateau is L(bol)~4200L_{sun} (scaled to the distance of the Galactic Bulge), corresponding to stable nuclear burning on a 0.6M{sun} white dwarf. A stable wind is blown-off at FWZI~1600km/s, with episodic reinforcement of a faster FWZI~3400km/s mass-loss, probably oriented along the polar directions. The collision of such winds could power the emission detected in X-rays. The burning shell has an outer radius of ~25R{sun} at which the effective temperature is ~7600K, values similar to those of a F0 II/Ib bright giant. The Delta(m)<1mag variability displayed during the plateau is best described as chaotic, with the irregular appearance of quasi-periodic oscillations with a 15-17 days periodicity. A limited amount of dust (~3x10^-11^M{sun}) continuously condense at T(dust)~1200K in the outflowing wind, radiating L(dust)~52L{sun}_.