Description:
------------
In one of my legacy websites, I'm using XSLT using the `XSLTProcessor` class from the xslt extension:

function process() {
    $xslt = new XSLTProcessor();
    $xslt->importStylesheet($this->xsl);
    foreach ($this->params as $name => $value) {
        $xslt->setParameter('', $name, $value);
    }
    return $xslt->transformToXML($this->xml);
}


The XSLT stylesheet I'm using also does some includes, with paths relative to the executed PHP script:

<xsl:include href="assets/xsl/basic.xsl" />

However, since migrating to PHP-FPM, I've found that sometimes, the worker processes get into a state where some workers work correctly, however some workers fail to find the included XSL sheets, resulting in errors:

Warning: XSLTProcessor::importStylesheet(): I/O warning : failed to load external entity "/var/www/hebe.nl/http/assets/xsl/basic.xsl" in /var/www/hebe.nl/http/include/classes.sys.php on line 315

Warning: XSLTProcessor::importStylesheet(): compilation error: file /var/www/hebe.nl/http/ line 14 element include in /var/www/hebe.nl/http/include/classes.sys.php on line 315

Warning: XSLTProcessor::importStylesheet(): xsl:include : unable to load /var/www/hebe.nl/http/assets/xsl/basic.xsl in /var/www/hebe.nl/http/include/classes.sys.php on line 315

When restarting PHP-FPM, the problem fixes itself, but that's not a very nice way to solve it. :)

Expected result:
----------------
XSLT includes should work (or not) consistently.

Actual result:
--------------
Reloading the page sometimes results in the correct HTML, sometimes has errors.