Indexing issue in OUtlook

Usually the Outlook index needs little maintenance, however, what I would do on the problem machines is:

Run chkdsk to make sure your drive is ok
Go to the control panel and select Indexing Options.
Select Outlook and click the advanced button.
Under settings take the rebuild option.

Sometimes indexing gets stuck and this helps.
Also, check for what is being indexed on the PC. You shouldn't be indexing everything as it makes the index very large.

If that doesn't work, turn off all indexing. Then turn on

This EE thread is directly related to your issue and has been solved by rebuilding the search index.

https://www.experts-exchange.com/questions/28370911/Indexing-issue-Windows-7-Outlook-2010.html

You might wish to remake your local OST file and once that has completed, re-index again.

So start this morning, remake the OST file (normally takes a while). At the end of the day, go to Control Panel, Index options, make sure Users and Outlook both show in Locations and then go to Advanced and Rebuild the Index. Let it run overnight and check tomorrow morning.