Thanks for the suggestion. As mentioned below by Jerome it's possible to scroll sideways with the Shift key. For quickly moving around large diagrams you can also use the Pan/Zoom window. Some other good tips are mentioned in this article as well.. https://www.orbussoftware.com/blog/panning-and-zooming-in-visio-2013/
Thanks for your feedback! Sorry to hear that you are encountering this issue, would it be possible for you to share the diagram, or a screenshot so that we can look into this. Increasing the support for shapes and diagrams is part of our roadmap.