If you're not having an additional issue, flickering normally happens when you cross Freesync minimum limit. Though in your case it's more likely that you're exceeding the maximum - because the games you listed are less demanding than the games where you don't see flicker. Try turning Vsync on. If it doesn't help, try a frame limiter - limit the games to ~136 fps or so. Either FRTC or Chill in Radeon Settings or RTSS (comes with MSI Afterburner). Try to install the monitor driver, if available.