The following issues have been identified with the link icon we provide (shown below) that opens the issue navigator and auto sets the JQL to
There are scenarios that the "sprint" field is not empty on an issue but it is still in the backlog.
e.g. a sprint is closed with an open issue, and upon closure, you select to move the issue to backlog instead of a different sprint.
If the original board filter contains any ORs in the JQL, the simple addition of the "and sprint is empty " text will only apply to the last part of the OR, and not any part before the last OR