Today a user was having an issue with regards to a beam not showing up in a plan view. Once the beam was placed, you could access the properties of it while it was still selected and see that the beam was definitely in the model and at the same location of the beams adjacent to it that were displaying properly in the view. When I went to their desk I walk through all the steps, and yes, as described the beam was being placed properly but it was not displaying in the view.
My first thought was to switch to a 3d view to make sure that is was where its properties was saying it was located. As we were switching to the 3d view I noticed that the active workset was set to the "Linked Revit Model - MEP" workset. The display of this workset was currently turned off in the plan view where the beam was not showing up.
Problem Solved!! Once we turned the workset on we found 4 beams placed on top of each other. (I bet if we placed it one more time it would of showed up) This is something that we come across every now and than and is on my list of things to check when elements do not display as expected. Remember to keep your eye on the active Workset if you have Worksets enabled.