Each time SketchUp is launched, plugins are displayed this way (see image). What to do to keep them in their place?
Typically this behavior is due to incorrect installation of SketchUp. Quit out of SketchUp, find the downloaded installer or download it again if you don’t have it. Right click on the installer and choose Run as administrator. Then, when given options such as Uninstall, choose Repair. Restart your computer after the repair has completed and then set up your toolbars in SketchUp.
To amplify on what @DaveR wrote, when you don’t install SketchUp correctly, one of the likely consequences is that some folders, files, or registry entries may fail to get permissions that let your SketchUp save things there - e.g. the locations and state of extension toolbars.