Looks like a shading error with triangulated or non square faces. At least, i have some similar problems with latest version of RPR:
https://community.amd.com/message/2926351?commentID=2926351%23comment-2926351
Kind of lost, why would a non-square UV or a face make such problems
Please attach a scene.
Sorry but i no longer has the scene as it was.
Right now its a single face but from what i have noticed, it seemed like the Normal Map with the non-square faces were giving that effect, as seen in the 1st Post. It was acting up with any normal map, i mean plugged into any normal map circle on the Uber shader, reflection or coating or even Diffuse.