We’ve seen some issues on Windows 10 where recent updates are causing the Select tool to have some lag. We have a potential fix for SketchUp Pro 2018 (does not apply to 2017). Please download and run this script to apply the fix to SketchUp Pro 2018: https://goo.gl/srRuzB
Please let us know in the form if you have any questions. If you do want to disable the fix, please download and run this script: https://goo.gl/qRBVfH (Please make sure SketchUp is closed when you run the script).