XmlFileLoader issue, server configuration for hosting a prestashop site

Question

I've taken a Private Virtual Server (OVH) to give more space to an e-commerce site, but I'm struggling with its migration. Whether copying the version currently in production or installing the latest version, I encounter this error (see below).

I think it's related to a PHP module or a permissions issue, but I'm not sure what it is. I have php-xml installed. I've thoroughly checked my file permissions and owners. All the indicators in php-ps-info are green. Several Prestashop forum threads mention this kind of logs, but unhopefully nobody posted a solution.

Any help would be appreciated, I'm going around in circles and I'm sure it's something dumb...

Notice: Undefined property: DOMDocument::$documentElement in /var/www/dev/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php on line 590

Fatal error: Uncaught Error: Call to a member function getAttributeNS() on null in /var/www/dev/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php:590 Stack trace: #0 /var/www/dev/vendor/symfony/symfony/src/Symfony/Component/Config/Util/XmlUtils.php(89): Symfony\Component\DependencyInjection\Loader\XmlFileLoader->validateSchema() #1 /var/www/dev/vendor/symfony/symfony/src/Symfony/Component/Config/Util/XmlUtils.php(146): Symfony\Component\Config\Util\XmlUtils::parse() #2 /var/www/dev/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php(397): Symfony\Component\Config\Util\XmlUtils::loadFile() #3 /var/www/dev/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php(49): Symfony\Component\DependencyInjection\Loader\XmlFileLoader->parseFileToDOM() #4 /var/www/dev/vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php(162): Symfony\Component\Depe in /var/www/dev/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php on line 590

Answer 1

When I had this issue, it was related to multiple PHP versions installed on the server. I've now removed all PHP and Apache, and reinstalled all with last PHP version, and fixed the issue.

I am unsure as to the exact cause of this error.