I have the same issue on PHP 7.0.14.
Have to notice, the problem connected not only with WSDL loading but with any SoapFault.
Also, it is not only php_mod realted, can be reproduced in CLI.

Looks like after SoapFault happens GC stops to work at all.
Every single call of gc_collect_cycles() returns 0 instead of 1.

Test:
----------------------------------------
<?php
class MyClass
{
    public $me;
    public function __construct()
    {
        $this->me = $this;
    }
}

$b = memory_get_usage();

try {
    $s = new SoapClient("dummy.wsdl");
} catch (\Exception $e) {
    echo $e->getMessage() . PHP_EOL;
}

for ($i = 0; $i < 3; $i++)
{
    new MyClass();
    echo gc_collect_cycles() . PHP_EOL;
}

var_dump(memory_get_usage() - $b);


Expected result:
------------------------------------------
SOAP-ERROR: Parsing WSDL: Couldn't load from 'some.wsdl' : failed to
load external entity "some.wsdl"

int(0)



Actual result:
------------------------------------------
SOAP-ERROR: Parsing WSDL: Couldn't load from 'some.wsdl' : failed to load external entity "some.wsdl"

int(4168)