THIS is what a slipping wind-on leader looks like. Notice the gap between the knot on the fluoro and the wind-on nub connection. Those are initially tied together. If there is a gap, the leader is slipping a tad. It doesn't fail because the Chinese finger trap serves as a backup. But it is definitely time to cut this connection and redo it. If you don't, the fluoro line will continue to slowly creep out of the hollow core line until it does finally fail.
In 2 years this is the only one I've had slip.
From Wind-On Leaders