On some songs in notation view a slanted line sometimes appears above the treble clef.

You can see it here, starting about 12 seconds in and lasting until about 22 seconds.

https://www.youtube.com/watch?v=SiYuSzHWVh8&feature=youtu.be

Have I made a mistake trying to enter tied notes? I have been using a slur for this, with mixed results. Notice the strange upside down tie starting in the 8th bar. And it is right when that bar plays the the slanted line appears.