The first place to look: 3rd party ANYTHING. Especially plugins. Remove any and all and try again. OR try the same under a different/new user. If it's fine there, you know it's something with your user's install. It shouldn't be an issue and it isn't here.

Thanks for your feedback! Much appreciated.

It only shows when you have NOTHING selected. It's the "Active Clip Indicator". Selecting a clip makes it active!