The plugin has always had this limitation. So long as you have more than one light, you'll end up with incorrect shadows. This is because the plugin is a shadow caster, rather than a light caster. If one light casts a shadow onto another light, said light will be in shadow. Very strange, but so far sadly unusable for me.
Oh, ok, then I hadn't noticed before since when I tried multiple lights I did it only with the Light Height set to 0 ("infinitely" long shadows). I too find it weird the way the light (shadow) is being cast and I hope for a more robust solution in the (near) future. I understand that box2d does have lightning capabilities build in, but I doubt that Ashley will implement them any time soon. As I read in response to requests on other topics, keeping the box2d features updated and functional for many exporters is difficult to maintain. I guess that that's an other drawback for not having native exporter.
What about this post from earlier in the thread? Doesn't that solve the issue? The new shader is already included.
Since the problem seems to be related with the shapes on the shadow's polygons, I don't see how this shader can resolve those artifacts...