I have also had this problem since 19.4.1. 19.3.3 works at 144hz. I can recreate the problem on earlier drivers by adding an HDMI 2.0 block using ToastyX CRU utility.
i5 3570
Gigabyte Z77-D3H
Radeon VII connected to Asus VG278HE via Ati branded HDMI to DVI adapter
Windows 10 x64 pro