Disappearing bodies following a tuturial

In Kevin Kennedy’s day 3 tutorial, when I extend the hinge pin all of the hinge parts disappear. The only thing I noticed is that when the tutorial mouse hovers over the vertical line of the bottom box both that line and the top horizontal line are highlighted. On my desktop with the same hover, ony the vertical line is highlighted. Also, when I highlight the tangent line and the bottom box vertical line, no angle degree appears.