I hole lenovo ideapad 320 , Currently running at 18.04LTS mate. While watching film top of screen line came/screen flaring.
Intel HD graphics 520. Issue happen only watching video. No hardware issue. On win 10 no issue.
You might try the solution here: https://askubuntu.com/a/668590
Or in MATE-Tweak in the windows option choose marco (Compton GPU Compositor) in the drop box under Window manager.