Have any co-orbital exoplanet pairs been discovered (and not subsequently retracted)?
One example is Kepler-91b; early observations included strange light curve behavior. While follow-up observations seem to confirm that it is in fact a planet, rather than some other object, Placek et al. (2015) suggested that there is a Trojan "planet" ($M\sim.025\pm.019M_J$) at one of Kepler-91b's Lagrange points - either L4 or L5.

The authors believe that this explanation explains the light curve data much better than the single-planet model, as the unexplained dimming could be the result of a "secondary transit" by the Trojan planet, rather than a "primary transit". However, predictions of the daytime temperature of the secondary planet fall squarely about 5,000 K, which is close to the temperature of the surface of the Sun. Albedo calculations are also higher than expected (0.49).

Therefore, the authors state that the light curve may therefore be a false positive, and Kepler-91b does not exist - and nor does the hypothetical Trojan planet.

Trojan co-orbital planets have been the main focus of theoretical and experimental research so far; see Giuppone (2012) for more information.