Crossref plugin - Forthcoming issue (article in press) - publication date error

Describe the issue or problem
Dear colleague,
i have some problem with sending metadata to crossref, publication date exactly.
I am using forthcoming issue plugin, where we publish article in press, also we are using crossref plugin for metadata and DOI registering. In the last time we have a problem with DOi registering, because we get following status from Creossref XML export plugin:

Error: cvc-complex-type.2.4.b: The content of element ‘journal_issue’ is not complete. One of ‘{“http://www.crossref.org/schema/4.3.6”:contributors, “http://www.crossref.org/schema/4.3.6”:publication_date}’ is expected.

<?xml version="1.0" encoding="UTF-8"?>

<doi_batch_diagnostic status=“completed” sp=“ds4.crossref.org”>
<submission_id>1550002304</submission_id>
<batch_id>_1669279489</batch_id>
<record_diagnostic status=“Failure”>

Error: cvc-complex-type.2.4.b: The content of element ‘journal_issue’ is not complete. One of ‘{“http://www.crossref.org/schema/4.3.6”:contributors, “http://www.crossref.org/schema/4.3.6”:publication_date}’ is expected.

</record_diagnostic>
<batch_data>
<record_count>1</record_count>
<success_count>0</success_count>
<warning_count>0</warning_count>
<failure_count>1</failure_count>
</batch_data>
</doi_batch_diagnostic>

problem was identified as publication date, but forthcoming issue hasnt any publication date
in the past wasnt any problem but now yes
please can you inform me where is the problem, or requirements from cressref was changed?:

In tha past we have insteled OJS 3.2.1.4
today we have OJS 3.3.0.14

Thank you