When designing our Gantt chart, we noticed that Primavera P6 draws all relationship lines, even when the predecessor and successor are so far apart that they can not be on the screen simultaneously. As a result, there are many very long vertical lines that cover the Gantt chart and make it very hard to read. We realized that relationship lines are only valuable when you can see which activities are being connected; otherwise, they add noise and get in the way. So, in our Gantt chart, we only draw lines when the predecessor and successor could be on the screen simultaneously. If that is not the case, we will omit the line and draw an orange triangle on the predecessor to show that a successor line is hidden, as well as an orange triangle on the successor to show that a predecessor line is hidden.
If you need to know what the hidden successors (or predecessors) of an activity are, select the activity row in the table and go to the Selected Activity > Successors (or Predecessors) pane at the bottom of the screen. This pane will allow you to see all of the successors (or predecessors) together, and allow you to navigate to any of them with one click.