You have a linked model that you cannot select or move. You notice it doesn’t even highlight when you hover over it. You have verified it is not pinned, the workset it visible and editable and it is not in a group. What else could it be?
Scroll down for the answer…
Check for Design Options under Manage > Design Options. It is possible to create a Design Option Set, and place the linked file in this set. Because by default Exclude Options is checked, Revit does not select the linked file when you hover or click on it.
If you un-check Exclude Options you should be able to select the link. This approach is useful should you wish to additionally lock down a linked file from accidentally being moved.
Special thanks to Tim Wadlock for passing this tip along!