I can confirm that it is probably not specifically a lightdm issue. I have Lubuntu installed and am running lxdm, and it affects me. I have found a consistent way to reproduce this; whenever my laptop comes back from being suspended, the mouse cursor disappears; returning to the login screen restores the mouse cursor, and it remains working in lxdm after logging in again.
I can confirm that it is probably not specifically a lightdm issue. I have Lubuntu installed and am running lxdm, and it affects me. I have found a consistent way to reproduce this; whenever my laptop comes back from being suspended, the mouse cursor disappears; returning to the login screen restores the mouse cursor, and it remains working in lxdm after logging in again.
I am running 16.04.