Running as administrator is how I install all and run all my software. So I doubt this the issue.
I can remove the icon, and add it back just fine. However what I notice is that when I’ve added just the Sketchup Pro icons to the taskbar, and then remove them, the removing them leaves a blank space on the taskbar, which I can still right click on (after removal), but it gives me the option to “pin to taskbar” on the blank space. These only properly disappear when I restart windows. So something is definitely funny here.