Over past few weeks we have been inundated with calls in relation to search not working.
After trying all these updates:

  1. Rebuilt the index
  2. Deleted the index file and rebuilt
  3. renamed and copied the .pst file
  4. Tried a lot of “solutions” from forums

Ms have finally fixed issue:
Check for Windows update to see if there are any improvements. Please go to Start > Setting icon > Update and Security >Windows Update