Switching user glitches greeter screen

Hi, my issue is, as the subject line states: I switch users, i.e. without logging out, and the greeter screen glitches and becomes all but unusable. Parts of the screen will flicker, and user selection is impossible.

This is on Mint 18.3 xfce.

I thought the greeter may be the problem, so I changed slick-greeter for lightdm-gtk-greeter, but the problem persists.

Thanks for reading and I'd really appreciate hints as to how to solve this.