After upgrading my desktop system from 13.2 to Leap 42.1:
GUI mouse "works", but no visible mouse pointer (GPM mouse is OK).
Mouse (and keyboard) connected on USB
Graphics hardware by Intel.
It worked normally under 13.2 (with kernel-desktop). AFAICT the Leap 42.1
system has only kernel-default (and kernel-xen).

Then I configured repositories and ran "zypper up". It found more than 3100
packages to upgrade.
At some point during the zypper run, the mouse pointer appeared (white arrow on
KDE windows, black arrow on GNOME windows).
After reboot, no mouse pointer again.

Even actions which are supposed to change the mouse pointer shape don't make it
visible: for instance in ksnapshot, selecting "Take a new snapshot" makes its
window disappear, the crosshairs pointer isn't visible. Then clicking the mouse
makes the ksnapshot window reappear, the arrow (default) pointer is still not
visible. Similarly when moving the hot point between a "normal" area (default
cursor not visible) and a browser textarea (I-beam cursor not visible).

I can only see where the mouse is if it happens to be on a widget which changes
its look on mouseover, or by drag-select where that is possible. In the general
case I have to guess. Keyboard control is often (not always) possible, but
usually not easy (tabbing through to the desired widget is often quite
time-consuming).

This happens in both KDE and GNOME windows so I suppose the bug is in neither.
Xorg is my "best guess" at a component, feel free to move the bug as
appropriate.