OK, so it's still that same query. I don't understand why it's being called, but here's how I'm hoping we can find out. In qa-db.php, find the line beginning @error_log inside function qa_db_fail_error(). After that line, please insert:
error_log('PHP Question2Answer stack trace: '.print_r(debug_backtrace(), true));
Then do something that triggers the usual error, and then post here the recent Question2Answer lines from the web server error log.