We have an EE 2.7.2 installation with a search feature produces random results. Sometimes, a keyword that definitely exists on the site returns results when entered into the search box, but other times, it will produce a "no results found". Same keyword, same browser, different results.
Sometimes, if I search for the keyword four or five times, a result is eventually displayed. Other times, a keyword produces instant results from the first search. There's no rhyme or reason for the results.