The reason that is in your model is because it is inserted.

The reason it floats away from the design, is because the components have been dragged away from their positions. When you move components, Fusion can either keep track of the position (capture) or it can rebuild the model as it is assembled (before manually dragging the parts, or moving them) this is called Revert.

If you wish to get rid of that floating part, redo the design without inserting it. You could alternately right click on it and Break Link, then right click on the resulting component and use Remove. The delete command will seek to get rid of items from the point they are created, which for the floating ring is when it is inserted, so if you need the inserted information, delete will not allow keeping it.
Phil Eichmiller
Software Engineer
Quality Assurance
Autodesk, Inc.