I discovered the solution to an issue with my mouse cursor disappearing when using Synergy (software that allows multiple computers to share the same keyboard and mouse) If you are having a similar issue, I hope my fix below removes the problem.
I am running Windows 8.1 on both PCs involved. I noticed that my display settings were slightly different than one another in the Display setting found in Control Panel. Here is a screen capture of what that looks like:
In my case, the slider for modifying text size was “smaller” (as seen above) on one PC, but moved up a notch on the other. When I made both PCs use the same (in my case, “smaller”) the cursor appeared on both screens when switching back and forth.