OK, this sounds like a mutter bug... unless that weirdness in your Xrandr.txt is related:
eDP-1 connected (normal left inverted right x axis y axis) ... DP-1 connected primary 2560x1440+0+0 (0x152) normal (normal left inverted right x axis y axis) 600mm x 340mm This means the desktop is arranged primarily to fit your external monitor (DP-1) but the built-in screen (eDP-1) has no known position. So it may not update properly. This is too suspicious to ignore so would be the first thing for someone to look at. -- You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to mutter in Ubuntu. https://bugs.launchpad.net/bugs/1846201 Title: Rendering is delayed on laptop display (works in external display) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/mesa/+bug/1846201/+subscriptions -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
