SketchUp favicon URL has changed causing error and standard "document" browser tab icon.
Per Caroline in the public forum
This is the link: https://www.sketchup.com/sites/all/themes/sketch_www/favicon.ico
... it is currently ...
https://help.sketchup.com/sites/all/themes/sketch_help/favicon.ico
... which gives a 404 Not Found error.
Reference public forum thread:
https://forums.sketchup.com/t/favicon-seems-to-be-missing/57625/