The test failure is in radv, in test_cs_uav_store(). I think that's pretty definitely unrelated. I'm not really sure I can reasonably debug it.
Given the results we're seeing (i.e., we seem to be reading back the clear value instead of the expected value from the dispatch), there's a perhaps conspicuous lack of uav_barrier() calls in test_cs_uav_store(). Is there anything in d3d12 that allows us to omit these? On the Vulkan side, UAV clears are essentially vkCmdDispatch() calls.