All was working flawlessly until I installed the latest version of Pigments 3 (along with a Reaper update and a new install of NI Massive X). All of my other VSTis work fine, with the exception of NI Massive X and Pigments 3. It's possible that the Reaper update or the Massive X install right around the same time may be related to this as well. I tried resetting to the defaults in Arturia center, but it had no impact.
Whenever I load either Pigments 3 or Massive X in Reaper, the entire GUI slows down and even VSTis that work fine now exhibit the same behavior (GUI only updates every 1-2 seconds or so). Interestingly, NI Massive X works fine in Cubase Elements 9, but not in Reaper - even before I try to load Pigments. Pigments does not appear on my list of VSTis in Cubase Elements 9, so I can't say whether it works OK there or not.
My MacBook Pro is a Late 2013 2.3 GHz Intel Core i7 with 16GB RAM. It's plenty of power as I can load up and run a bunch of other VSTis simultaneously without any issues. Any help you can provide is greatly appreciated!