There have recently been some threads on this topic that might answer your question. Also, it was not in the features poll for 2.3, so no I don't think anyone is actively working on it. https://forums.luxcorerender.org/viewtopic.php?f=4&t=1728 https://forums.luxcorerender.org/viewtopic.php?f=4&t=18...
Test.zipYou can replicate the problem with a plane This is a known limitation/difference between CPU and OpenCL rendering: you need to connect the the bump mapping to the root Mix node, not to the 2 Disney sub-nodes. Just mix the bump map textures and connect the result to the bump socket of the ro...