Seems to be a Wacom issue, not a LR issue. I'll update here incase anyone with my settings finds the same thing happening. Cheers!
Wacom is up to date - maybe they aren't communicating well with the update. Anyone else have this same issue?
I can't shift click using my Wacom tablet in LR or PS. Super huge boo. Hopefully there is a fix because using a mouse and my tablet isn't fun.
It looks like this is a common problem, but I was lucky that I hadn't experienced it before. Now I'm stuck with a Wacom tablet that only half works. I found this feed if you want to find more info: Photoshop CC: Clone Stamp Tool (alt + click) not working properly. | Photoshop Family Customer Community
Yay! Found a fix - rolled back to a previous Wacom driver and EVERYTHING WORKS NOW. Hooray!
It's definitely the Wacom driver that's problematic. Follow these instructions and install the old driver... now my SHIFT/OPT/CMD keys are working properly again and I can use Lightroom and PS like the good old days.
They say the new driver 6.3.19-9 has fixed the issues, but apparently so many people are downloading that it crashed the entire Wacom server. 15-3 works relatively error-free.
Disconnect the tablet from the computer
Open your Applications folder and locate any Tablet or Wacom Tablet folders you have
Use the Utility in each of these folders and click ‘Remove’ under ‘Tablet Software’
Once the software is removed, restart the computer
Once this is complete, download and install the 6.3.15 driver from: