Mouse Double-Clicking in High Sierra

Ever since upgrading to macOS High Sierra (which was a massive pain that took nearly twenty reboots and six different methods, but that's a different story) my mouse has been double-clicking when I single click on things around the OS. This happens with every mouse or trackpad input I've tried; my built-in trackpad, Magic Trackpad, and wired USB mouse. I've tried the trackpads with the mouse unplugged, even the built-in one with the mouse unplugged and Bluetooth off... no luck. It doesn't even appear to happen all the time, but it's pretty consistent in a couple areas:

• Launchpad (opening folders opens the app in the folder that is in the mouse's position)
• Finder (clicking menubar items opens and then quickly closes the menu)
• Notifications (clicking "Later" on persistent notifications for Calendar or Reminders opens the app)
• iTunes (list view; clicking on editable fields a single time edits the field)
• Photos (I believe this is causing crashes when launching Photos due to multiple instances? Not sure)
• Photoshop CC (selecting tools brings up the list of additional tools, which happens on double-click)

Strangely, this does not seem to happen when clicking on text in Safari, Pages, Spotlight, etc at all; it only shows up in some places all the time, randomly other times throughout the OS including both first-party and third-party apps, and other times not at all. I was hoping the supplemental update would fix the issue, but it didn't. I've reported this to Apple but due to lack of matches on Google I'm guessing it's not a common issue and therefore is not likely to be fixed by Apple anytime soon.