Import XML does nothing in OJS

I’m trying to import a large collection of existing issues and articles into a new test journal. I’ve generated an XML file containing all the data, and that file is valid against the XSD schemas and seems complete to me. It links to the articles and associated images etc. using the href element.

I have the role of Journal Manager. I go to Tools / Import, and upload the XML file. Then I press Import, and all I see is an empty Results tab. There is no feedback of any kind, and nothing is imported.

When I first tried this, I did get reports of invalid id elements in the file; these were not invalid according to the XSD schemas, but were not important, so I deleted them and the error went away. So I know that the file is being parsed and validated, at least. But after that, nothing. The browser debugger shows:

[HTTP/1.1 500 Internal Server Error 223ms]

Internal Server Error
Transferred1.43 kB (0 B size)
Referrer Policystrict-origin-when-cross-origin

but only once; if it were failing to retrieve all the linked files, I’d expect to see it multiple times.

Application Version: OJS

I’m happy to share the XML file, which is about 1MB in size, if that will help. If the problem is that I’m linking to remote copies of images and articles, then I would expect to see an error message to that effect, in which case I would find a way to place the files on the filesystem (that’s not trivial because the journal is moving to another institution where I have no privileges except within OJS itself).

All help appreciated,
Martin Holmes