Crossref submission fails because Plugin expects parameter 1 to be string, array given [OJS 3.3.0.7]

Description of issue or problem I’m having:

Working with OJS 3.3.0.7 I am not able to submit DOIs to Crossref.
Crossref refuses to register the DOI due to a missing title, while the title is really there.

Registration was not successful! The DOI registration server returned an error: ‘Deposit contains title error(s): Title name value is missing from the title element (403 Forbidden)’.

Steps I took leading up to the issue:

Submitting a DOI to Crossref

What I tried to resolve the issue:

When I export the Crossref XML file and inspect it, I can see that the title, subtitle and abstract are indeed missing.

I have also checked the PHP log, results are below

Application Version OJS 3.3.0.7:

Additional information, such as screenshots and error log messages if applicable:

This is what the PHP log has to say about it.

[03-Jan-2022 11:48:39 Europe/Amsterdam] PHP Warning:  htmlspecialchars() expects parameter 1 to be string, array given in /Users/gemusehandler/Sites/ojs3307/plugins/importexport/crossref/filter/ArticleCrossrefXmlFilter.inc.php on line 100
[03-Jan-2022 11:48:39 Europe/Amsterdam] PHP Warning:  htmlspecialchars() expects parameter 1 to be string, array given in /Users/gemusehandler/Sites/ojs3307/plugins/importexport/crossref/filter/ArticleCrossrefXmlFilter.inc.php on line 101
[03-Jan-2022 11:48:39 Europe/Amsterdam] PHP Warning:  strip_tags() expects parameter 1 to be string, array given in /Users/gemusehandler/Sites/ojs3307/plugins/importexport/crossref/filter/ArticleCrossrefXmlFilter.inc.php on line 165

Hi @Franklinx,
the problem was solved?

Not completely. I have done a lot of testing and the issue seems to result from importing one new journal into the OJS of an existing journal. The separate journals didn’t have a problem with submitting to Crossref.
In the end I have decided to keep the journals apart and give them both their own OJS and move on. After that I forgot completely about the issue