I had an issue with my external HD monitor which started flickering and the rows of pixels were unaligned with each other a bit so the picture was kind of blurry. I tried everything from changing some settings to a different kernel and nothing worked.
Make sure your monitor refresh rate and settings match.
Go to Settings > Devices > Displays
Check your monitor maximum Hz (do not include freesync or other support only base maximum Hz.)
Make it same for example if your monitor supports max 60Hz and 75Hz with freesync, then go to settings and make it 60Hz.
I've similar problems with my monitor&Ubuntu18(laptop). After some investigation, I fixed this problem and found the root cause in my environment.
My problem's root cause is in the HDMI signal quality, and the HDMI signal poor quality has two root causes:
- The HDMI cable;
- The HDMI cable doesn't plug into the socket closely;
My final solutions are as:
- Re-plugin the cable with your PC and monitor, and secure them carefully;
- Buy and use a new high-end HDMI cable(above 20$, seller should claim it support 4K or 8K);
- If you couldn't do the 2nd solution, and the problem still exists, lower your display configuration just like the solutions provided by others in this issue, e.g. lower the display resolution to 720P, or lower the display frequency. These lower resultion doesn't require high signal quality transferring capability in your cable, so they could work without problem.