Regularly, when I am using Photoshop CC 2018 (mostly), suddenly I got a modifier key which always stays activated. Sometime it is the Command key, and sometimes Shift key, which make it impossible to work with these kind of applications using modifiers keys intensely the for almost anything.
The only way is reboot, but even so, I suspect that when I have rebooted and relaunched Adobe Photoshop, the mean bad appends very quickly, so very hard/almost impossible to work.
Here's my configuration:
MacPro 4,1 (Nehalem) running OS X El Capitan 10.11.6
Adobe CC 2018 Suite
Also, I have a Wacom Intuos4 Tablet, (actually with driver 6.3.32-4), but I got the bug since several previous version of the Wacom Tablet driver, and (surprise) a mouse and a keyboard.
Worth mentioning: the keyboard is actually a Window keyboard, but it didn't need any driver to install. I just got few key not related to Mac function, but even the F1 to F15 key function work as intended by Apple when using it with the Fn key (Sound Up/Down/Mute and Mission Control etc...).
Let me know if you need a EtreCheck Report, (?) if so I can quickly post a link of my current report.