I can't (or at least don't want to) imagine using the software without the orange highlight under my cursor to show me what I'm about to select.  To turn it on go to Tools > Options > System Options > Display/Selection and check the box for “Dynamic highlight from graphics view”.  If you had this turned on, and it turned itself off, it’s almost certainly your 3d mouse.  The 3dconnexion software temporarily turns off dynamic highlighting while the 3d mouse is manipulating a model to prevent multiple edges and faces being highlighted as they move across your cursor.  It's supposed to turn it back on when you release the 3d mouse, and it usually does, but not always.  A few years ago I might have it happen two or three times in a day, then not again for weeks or months, but it's definitely gotten better in recent years.

 

If it happens to you often enough to be a problem please go to 3dconnexion's technical support site.  I've dealt with them a time or two on other issues and gotten good results.