What PCI-E lanes are you using?
Are they both running at x8 speed?
Do you have any other devices in any PCI-E lanes?
Are both GPUs detected in Radeon Settings and Device Manager?
Have you tried updating Bios to the latest revision and using Bios default settings?
As there has been no update on this thread, I am locking the discussion. If you are still experiencing the same issue, please start a new discussion and provide the essential information required. https://community.amd.com/thread/196209