Comment 97 for bug 1581088

In my case, same thing than above: Logitech M310 middle button not working on Ubuntu 18.04 => issued "xev | grep button" on a terminal, checked the left, then the right and finally the middle/wheel buttons:
# xev | grep button
    state 0x0, button 1, same_screen YES
    state 0x100, button 1, same_screen YES
    state 0x0, button 3, same_screen YES
    state 0x400, button 3, same_screen YES
    state 0x0, button 2, same_screen YES
    state 0x200, button 2, same_screen YES
    state 0x0, button 2, same_screen YES
    state 0x200, button 2, same_screen YES
Then, just after closing the xev window, noticed the "middle mouse button click/paste" suddenly started to work again. Weird...