Having run into "my *entire* list of clients vanished?!?!?!" situations, the FIRST thing that you do is check to make sure that you do NOT have any kind of Filter applied in the left-side panels.
  (I was on "All clients" in the second panel...  but had managed to accidentally click on the "EFile Clients" in the top panel.  At the beginning of tax season, we had NO clients who were considered efile yet, so...  everyone vanished!)



Robert