Mysql insert not saving

Hi,

I am having trouble saving a row to the DB. I have a plugin that i have modified slightly (added one extra column in the DB table). When it saves to the DB, the query returns successfully and has a value of the ID (auto-incremented in MySQL), but the row does not get saved. The code is fairly vanilla:

$query = $wpdb->prepare($query, $values);
$query_results = $wpdb->query($query);
if($query_results) {
  return $wpdb->insert_id;
}

So this works for two other calls in the same form action, $wpdb->insert_id contains the next valid auto-id, but no rows are in the DB. I have tried turning on all the logging I can, and there are no errors at all. $wpdb->show_errors(); has no content.

Also the SQL seems to be OK – I can use the text from $query or $wpdb->last_query in a DB window and they work fine, and insert a row that I can see.

I was guessing there was a transaction on that table, so copied the DB to a new one and reran, but had the same results.

I am not sure how to debug this further. I don’t have access to the error logs in the DB itself as it is on a shared host.

The server is MySql 5.6.34, PHP 5.6.28.

If anyone has any ideas or tips on moving forward, please let me know.

Thanks!