I upgraded an 2.4.3 installation to 2.4.8.2 and then to 3.0.2. No problems there.
However, when I tested the xml export I noticed that exporting one of the issues created errors (line numbers could be a bit off):
[Fri Mar 17 13:02:06.886444 2017] [:error] [pid 19146] [client 192.xxx.xxx.xx:xxxxx] PHP Notice: Undefined offset: 18 in /var/www/ojs/public_html/lib/pkp/plugins/importexport/native/filter/SubmissionFileNativeXmlFilter.inc.php on line 79, referer: http://domain.fi/index.php/journal/management/importexport/plugin/NativeImportExportPlugin
[Fri Mar 17 13:02:06.902584 2017] [:error] [pid 19146] [client 192.xxx.xxx.xx:xxxxx] PHP Notice: Trying to get property of non-object in /var/www/ojs/public_html/lib/pkp/plugins/importexport/native/filter/SubmissionNativeXmlFilter.inc.php on line 285, referer: http://domain.fi/index.php/journal/management/importexport/plugin/NativeImportExportPlugin
[Fri Mar 17 13:02:06.902607 2017] [:error] [pid 19146] [client 192.xxx.xxx.xx:xxxxx] PHP Fatal error: Call to a member function getAttribute() on a non-object in /var/www/ojs/public_html/lib/pkp/plugins/importexport/native/filter/SubmissionNativeXmlFilter.inc.php on line 285, referer: http://domain.fi/index.php/journal/management/importexport/plugin/NativeImportExportPlugin
After some debugging I found that the error is caused by a submission file with file_stage 18. After chancing that to 10 the xml export works. @bozana, I wonder where the 18 is coming from? The file and all it’s revisions had it. No other file does.