CrossRef XML Export Plugin problem

Describe the issue or problem
After the upgrade from OJS3.1.2.4 to OJS3.3.0.13 we realized that the doi deposition to CrossRef does not work anymore. In the previous version, it worked perfectly.

Steps I took leading up to the issue
The CrossRef Export Plugin does not show the list of articles in the Article tab. Instead, it displays a “Loading…” as though it loads the articles but looks like an infinite loop.

What application are you using?
OJS 3.3.0-13 (after the upgrade from

Additional information
In the error_log I found the following part, which might be related to the problem:

[20-Feb-2023 21:41:30 Europe/Zagreb] ojs2: 404 Not Found
[20-Feb-2023 21:44:09 Europe/Zagreb] PHP Warning: Cannot modify header information - headers already sent by (output started at /home/iapchemo/public_html/pub/ojs/lib/pkp/plugins/generic/acron/ in /home/iapchemo/public_html/pub/ojs/lib/pkp/classes/plugins/ on line 178
[20-Feb-2023 21:44:09 Europe/Zagreb] PHP Fatal error: Uncaught Exception: Could not convert selected objects. in /home/iapchemo/public_html/pub/ojs/lib/pkp/classes/plugins/
Stack trace:
#0 /home/iapchemo/public_html/pub/ojs/classes/plugins/ ImportExportPlugin->displayXMLValidationErrors(Array, ‘<?xml version="…’)
#1 /home/iapchemo/public_html/pub/ojs/plugins/importexport/crossref/ PubObjectsExportPlugin->exportXML(Array, ‘article=>crossr…’, Object(Journal))
#2 /home/iapchemo/public_html/pub/ojs/plugins/importexport/crossref/ CrossrefInfoSender->_registerObjects(Array, ‘article=>crossr…’, Object(Journal), ‘articles’)
#3 /home/iapchemo/public_html/pub/ojs/lib/pkp/classes/scheduledTask/ CrossrefInfoSender->executeActions()
#4 /home/iapchemo/public_html/pub/ojs/lib/pkp/plugins/generic/acron/ ScheduledTask->execute()
#5 [internal function]: PKPAcronPlugin->shutdownFunction()
#6 {m in /home/iapchemo/public_html/pub/ojs/lib/pkp/classes/plugins/ on line 189