The Mouse Disappears after unlock problem is not common error and I’ve just faced it when using light-locker / lightdm combined with XFCE4. Each time my screen goes blank after idle time is reached and I relogin, the mouse pointer becomes invisible but active. You can still move the mouse and you can see (because it highlights the window) as you move it around and you can click and right click but the cursor is not displayed on the screen. If I restarting the Xserver, everything backs to normal, but I lost my working session.
After researching on the Internet about this problem, I find the cause of this problem is light-locker package. I’ve tried to remove light-locker and boot my system with gdm and xscreensaver packages installed. It’s working flawlessly without disappeared of mouse after relogin.
This has been a known issue for some time with light-locker and xorg-x11-server. You can read more about it at #815135, #80, #94677… There are bug reports all over the place but no solution yet, e.g. In my exprienced, it’s depended on your system hardwares (Intel graphics) and linux distros (using XFCE4 as Desktop Environment). It’s fixed on my laptop after light-locker upgraded to newest version but my home station is not yet. This is often observed in systems that lock the session and return to the greeter (including at least Xubuntu, Ubuntu Mate, and elementary OS).
Here are some methods that will help you solving it.
Permanent Method
Switch to another lock screen and windows manager packages instead light-locker or upgrade / downgrade it until this problem fixed.
Temporary Method
$ xset dpms force off Quick press any button to active and light on your screen, you will find your mouse pointer restored again.
Another way will help you restoring the mouse pointer by switching to another virtual screen TTY for example Ctrl + Alt + F1 then back to the Ctrl + Alt + F7
Another hard way is switch your mouse cursor theme will restore the pointer again.
Notes: Don’t use lightdm build-in lock screen utility by dm-tool switch-to-greeter or dm-tool lock command, because the lock screen can be circumvented by switching to console.