My iphone X with latest iOS says 'Location Shared by another device' but I have no other device
Once upon time, not long ago....

You shared your location with Family or with a Friend.

How to remove old friends from sharing location ?

Launch the Settings app on your iPhone or iPad.

Tap on Privacy.

Tap on Location Services.

Tap on Share My Location.

Tap the friend you would like to remove

Tap Stop Sharing Location