Sometimes when I reboot or turn on my machine, at the login page the mouse is simply gone, I can login and still have the same problem, after rebooting the problem is gone, but after a few reboots it happens again. I am using the coreboot firmware of starlabs.
I am using gnome, and it’s a fresh install, it was manjaro minimal gnome installed monday. My hardware is a starlabtop mkiii.
Exactly the same thing happens to me. I find it a minor irritation so have not looked into it. Using xfce.
To reboot I use Ctrl+alt+t then enter reboot. Every now & then I have do that twice.
Welcome to the forum! 
Please post your system info as outlined here:
@Hipster Please create your own topic as you may have a different mouse and are running a different Desktop Environment and Login Manager.
Are you using dual/triple monitors? The cursor may be in an area, where the monitors are supposed to be. You may check the greeter settings if the above situation is applicable.
It’s a latop, only the laptop screen