Valid MySQL Delete Query returning non-object - php

Question

This one's a mystery to me and no one that I've read up on so far has had this issue, and I'm losing my mind here, so here goes. I'm trying to run this simple query from php on a mysql database with a user that has all required privileges (usually there is more than one entry in the ID array):
$sqlDelete = 'DELETE FROM wsa.customers WHERE `id` IN (18)';
$result = $conn->query($sqlDelete);
When I run this code from phpmyadmin and workbench this executes just fine, but not using php on the server (though it does handle updates and inserts without issue).
The $result is not a result object (though it should be) and I see no error or warnings at all...everything is as if nothing went badly though the user is obviously not deleted.
I'd just like to get input on where I should be looking as this is not a syntax issue....I've run out of ideas.
Thanks
UPDATE ON SCHEMA QUESTION:
CREATE TABLE `agreements` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`created` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
`creator_id` int(11) NOT NULL,
`term` tinyint(4) NOT NULL,
`contractDate` date NOT NULL,
PRIMARY KEY (`id`),
KEY `creatorid_idx` (`creator_id`),
CONSTRAINT `userid` FOREIGN KEY (`creator_id`) REFERENCES `master`.`login` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=latin1;
CREATE TABLE `customers` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`agreement_id` int(11) NOT NULL,
`name` varchar(128) NOT NULL,
`plan` varchar(255) NOT NULL,
PRIMARY KEY (`id`),
KEY `agreementid_idx` (`agreement_id`),
CONSTRAINT `agr_id` FOREIGN KEY (`agreement_id`) REFERENCES `agreements` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=21 DEFAULT CHARSET=latin1;
UPDATE 2: Connnection Details:
$dbhost = 'localhost';
$dbuser = 'xxx';
$dbpass = 'yyy';
$conn;
$conn = new mysqli($dbhost, $dbuser, $dbpass, 'wsa');
if ($conn->connect_errno) {
echo "Failed to connect to MySQL: (" . $conn->connect_errno . ") " . $conn->connect_error;
}

Answer 1

Sorry folks...in the end I was erroneously using if(!result) to test whether the query went through on a previous insert query to the one shown and it was causing the whole transaction to fail. My apologies. Thanks to #Darwin von Corax for pointing me in the right direction.