can you list the types of maps your exporting from substance. roughness, bump, normal, ect also format of textures might be needed to know.
i will try to reproduce it.
We have a known issue when using texture maps in the Metalness connection of the RPR Uber Material. I'm not sure if this is the issue you are experiencing.
I will try another scene and revert. If what I'm doing is wrong then perhaps now is a good time to shed some light on a proper workflow from substance to pro render?