Disappearing Square Comment tool.

I have a user that regularly uses Adobe Acrobat DC, and he's got a persistent issue (now on 2 computers) with this square comment tool disappearing, the actual tool turns invisible when you mouse over it, then when you select it, your cursor disappears, and any squares you make turn invisible after being created.
I've logged into this computer on my account, and haven't had the same issues- so I assume that it's local to the profile.
Troubleshooting performed:
Uninstalled/reinstalled Adobe DC
Perforned a repair installation
Uninstalled, deleted all local (C:\Users\USER\AppData\Local\Adobe and C:\Users\USER\AppData\Roaming\Adobe) adobe files, then reinstalled.
I've reset the tool bar a dozen times.
I'm running out of ideas. The tool even disappears when creating a custom comment toolbar, and mousing over the square tool in there.
Any ideas?