I recently installed Radeon™ Pro Software Enterprise Driver 17.Q4.
After a reboot my 4K monitor was recognized as 1080p.
Turning on virtual super-resolution in AMD drivers panel was a half measure as the resolution was upscaled and it didn't look good.
I performed a clean install of 17.Q3.1 version and everything went back to normal.
OS: Windows 10 64 bit updated daily.
Monitor: Acer CB271HK - connected via DP.