Try to lower the refresh-rate of your display, from 144 hz to 120hz, or 75 hz to 60 hz (etc).
Have the same thing with a 1440p 75 hz monitor. Have to lower it from 75hz to 60 hz, the "funny" thing is that with this same monitor, on a RX 590 or Vega 64, the memory clock downclock properly on idle state.
I plug another monitor FHD 60 hz and memory droping to 200 mhz. There is in driver problem only.