I discovered a bug. Tested this in a portable install. As soon as I install the plugin and enable my LaunchPadX, I get the problem.
Here is my project:
https://drive.google.com/file/d/1-jO...ew?usp=sharing
After enabling the plugin, I'm getting about half second freezes of the whole Reaper UI every couple seconds. Disabling all plugins makes it go away, but enabling them one by one incrementally causes it to return. Even moving faders with mouse or MIDI controller exhibits these little delays and it isn't purely visual as the audio follows the actual fader movements.
Actually this has be driving me nuts for months because I was sure it was some plugin, but finally I tested it today in a portable install and ruled out my REAPER.ini and the plugins in the project. Next I looked at UserPlugins and found that deleting this one fixed it.