Hi
I had the same problem with the 3.1.1.1 version and I changed row 102 and 103 in https://github.com/pkp/ojs/blob/ojs-stable-3_1_1/plugins/importexport/crossref/filter/IssueCrossrefXmlFilter.inc.php
to
$headNode->appendChild($node = $doc->createElementNS($deployment->getNamespace(), 'doi_batch_id',htmlspecialchars($context->getSetting('initials', $context->getPrimaryLocale()) . '_' . date("YmdHi"), ENT_COMPAT, 'UTF-8'))); $headNode->appendChild($node = $doc->createElementNS($deployment->getNamespace(), 'timestamp', date("YmdHi")));
where time() was replaced by date(“YmdHi”)
Maybe this can be an option for future releases to choose format of timestamp?