I think it is limited or mainly in the canvas (a little bit hard to tell as it is so distracting), but it appears ONLY on the iPad Pro display, not on my MacBook’s screen, even when I am using the Apple Pencil on the iPad Pro.
I only use the Apple Pencil, but it happens with the sliders AND with certain local brushes (the radial and graduated filter are the most prominent).
No new equipment other than the switch from Xrite to Datcolor Spyder (and it does not matter if the Spyder is connected or not). I have also tried using different USB cables and different 3.1c adapters–no change.
I have tried setting LR to use Smart Previews (maybe slightly better–not much). I have tried turning off the Graphics Processor on the MacBook (no change on the iPad). I have tried different levels of iPad display brightness, tried turning Wi-Fi and AirPlay off–no difference.
Mac OS and iOS are both autoupdated to latest versions. OS-X 10.12.6 (16G29) on the Mac, and problem happened with both the last version if iOS 10 and continues on iOS 11.0.2