The problems seem to be solved if I create the file /etc/X11/xorg.conf.d/20-intel.conf with, inside:
Section "Device" Identifier "Intel Graphics" Driver "intel" Option "AccelMethod" "sna" Option "TearFree" "true" EndSection It seems to fix the symptoms I described before and other symptoms that appeared at the same time (but less frequently): * characters disappearing in some windows, for example in emacs, firefox, chromium tabs and URL bar * freezes
