When i search a keyword in search from in Magento 2 version it shows the following error. Syntax error or access violation: 1064 syntax error, unexpected $end, expecting FTS_TERM or FTS_NUMB or '*'.
i have searched in DB with my searches keyword and i found it in a table name "search_synonyms". there are some other data was exist in the table. i also make some search with the text take from the table and i get same error in magetno front end again. the text was in the field "synonyms" is hat "hats". the double coated text is making problem in the search in Magento front end.
i removed all of data from table "search_synonyms" and my search are working with the keyword thats makes problem age.
you can try it. if your problem same as my this problem you may get a solution.