I have by now tried atleast 25 different "fixes" for this problem, but none of them work for me, with either GPU.
I am getting a very similar issue, I have found that if I go back to previous WQHL release it will work just a shame that you can't run the latest drivers.
Mobo bios updated ?.
Bios settings to match the 380(legacy/uefi) ?.
Old drivers removed (use DDU) before inserting new card ?.
Graphics drivers on hard drive with OS.
Have you tried Clean Install AMD Graphics Drivers