Why did error messages change after upgrading to MySQL 5.7.9?
An off-the-wall guess:  You have a column (or something) that matches a new reserved word.

5.7 adds GENERATED, OPTIMIZER_COSTS, STORED, VIRTUAL as "Reserved" words, plus a number of "non-reserved" words.  Details in keywords.html.

In some contexts, use of a keyword can lead to a cryptic error message.  When you find the context, please file a bug report at http://bugs.mysql.com .

Another tip:  Search for 1054 in your sources, then look at what immediately precedes it.