Which AC version are you actually working on?
Suggestion 1 :
AC10 + AC11 : please check View > Elements in 3D view > Filter Elements in 3D : choose Infinite or modify settings "From story ... to story..."
If previous AC version : see Image > Elements to show in 3D...
Suggestion 2 :
Do you have different Layer Combinations for 3D views and section / elevation? If so, check layer settings !