The mouse cursor image sometimes vanishes.  Restarting X11 (with either
control-alt-backspace or /etc/init.d/gdm3 restart) does not bring the
cursor back.  The mouse still *works* - I can click on things or hover
over things, I just can't see the cursor.  Disconnecting and reconnecting
pointing devices (Wacom Bamboo and a USB mouse) does not have any effect.
The cursor will reappear if I reboot the computer, or if I set
Option "HW_Cursor" "off" in xorg.conf; however, using the software cursor
triggers bug #634082.

The video card is an embedded on-motherboard device.

The cursor will become visible if I use the fbdev driver instead of the
nouveau driver  (Presumably, fbdev cursors are always software?).  Once
the cursor has disappeared, rmmod -f'ing nouveau and using the non-free
nvidia driver does not bring it back, however.

Sometimes I'll notice it after an hour or so using my computer, sometimes
it won't show up for days.  I often have multiple X servers running at
once, which might be exercising the bug.  I haven't yet determined a
reliable way to reproduce it.

I believe I also observed the disappearing cursor bug using the nv driver
on another computer, but at the time I thought it was a hardware problem
and so did not gather the data necessary to properly report it.

I suspect that this bug may be related to
https://bugs.launchpad.net/xorg-server/+bug/63905 .