Code creates two MySQL rows instead of one - php

Question

I´m trying to create just one new row in a MySQL table
The problem is that I´m getting two new rows in my database.
I really can´t see why this is happening. The debug_to_console( "makepass" ); - my debug function - only gets executed once? AND the two rows it creates is not identical/copies
debug_to_console( "makepass" );
$salt = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
$len = strlen($salt);
$makepassJBH = '';
for ($i = 57; $i < $len; $i ++) {
$makepassJBH .= $salt[mt_rand(0, $len -1)];
}
$newpassJBH = password_hash($makepassJBH, PASSWORD_BCRYPT );
$licensidentifierJBH = '';
for ($i = 57; $i < $len; $i ++) {
$licensidentifierJBH .= $salt[mt_rand(0, $len -1)];
}
$fullkey = $makepassJBH . $licensidentifierJBH;
try {
// Get a db connection.
$db = JFactory::getDbo();
// Create a new query object.
$query = $db->getQuery(true);
// Insert columns.
$columns = array('licenskey','licenskey_Identifier','dateCreated', 'printed');
// Insert values.
$values = array($db->quote($newpassJBH), $db->quote($licensidentifierJBH), $db->quote(date("Y-m-d")), $db->quote(0));
// Prepare the insert query.
$query
->insert($db->quoteName('#__licenskey'))
->columns($db->quoteName($columns))
->values(implode(',', $values));
$query .= ' ON DUPLICATE KEY UPDATE ' . $db->quoteName('licenskey_Identifier') . ' = VALUES(' . $db->quoteName('licenskey_Identifier') . ')';
// Set the query using our newly populated query object and execute it.
$db->setQuery($query);
echo $db->replacePrefix((string) $query);
$db->execute();
}
The SQL dump:
INSERT INTO `mdh_licenskey` (`licenskey`,`licenskey_Identifier`,`dateCreated`,`printed`) VALUES ('$2y$10$jXkjJX1OZ7Vu0okV/QlxcehF5T2SSPZFhVHIx.E64HhidgYY.3URS','juLEo','2018-07-23','0') ON DUPLICATE KEY UPDATE `licenskey_Identifier` = VALUES(`licenskey_Identifier`)

Answer 1

Since the license key is generated by the PHP code above, that code must be executed twice. This can happen for multiple reasons but it can be difficult for us to guess exactly why. Either check if your browser is calling it twice, or if it is called twice from within the PHP code.

Answer 2

Make sure your script isn't executed twice. I had this issue when using firebug for example. This plugin made my page execute twice but not outputting to the console.
Sort of like a "prefetch" of the page before showing, don't know for sure.
Maybe add a 'debug to console' point on every line, like 'here 1, here 2'..