Thank you for this bug report. To properly diagnose the problem, we
need a short but complete example script to be able to reproduce
this bug ourselves. 

A proper reproducing script starts with <?php and ends with ?>,
is max. 10-20 lines long and does not require any external 
resources such as databases, etc. If the script requires a 
database to demonstrate the issue, please make sure it creates 
all necessary tables, stored procedures etc.

Please avoid embedding huge scripts into the report.

An array of Traversables?

<?php

$dom = new \DomDocument;
$dom->loadHTML('<span>ONE</span><span>TWO</span>');

$xpath = new \DomXPath($dom);     # $xpath -> \DOMXPath
$nodes = $xpath->query('//span'); # $nodes -> \DOMNodeList


# this works:

foreach ($nodes as $node)
{
	echo $node->nodeValue; # \DOMElement
}


# this not:

array_column($nodes, 'nodeValue');

?>

As is documented, array_column (and other array_* functions) take arrays as inputs. $nodes is not an array. Use iterator_to_array() to convert.

If you want something changed on the PHP side then you should raise the subject on the internals mailing list because whatever it is likely won't be trivial.
http://php.net/mailing-lists.php