After upgrading to magento 1.9.3.1 the search bar for typing the search shows the search terms so it is clear it has results but then the results page says "Your search returns no results."
We've got a fix for it that works. If you copy this fix into app/local/Mage/CatalogSearch the system will work like before.
Click here to download the fix in zip format
Note : Don't forget to reindex !
Magento 1.9.3.1 and linux terminal / comandline Reindex