Lately I experienced problems using alt+tab for switching between applications in manjaro-linux using mate-desktop. The problem seems to be the little thumbsnails showing a current preview of the specific application.

To get rid of the problem:

Pererences > Windows

Uncheck 'Enable software compositing window manager'

Ref: https://makandracards.com/makandra/47066-ubuntu-mate-fixing-alt-+-tab-being-really-slow