OJS publication galleys inaccessible and missing PDF icon in article

Hi, We are running OJS on RHEL 7.9 with mysql 5.6
We have a journal with one article in particular for which the publication galleys are no longer accessible. The article was loaded via QuickSubmit in an older version of OJS (2.4.8 I believe).

There is no submission file in the Workflow submission tab on our DEV, QA or PROD instances. There is a productionReady file on PROD, but none on QA or DEV. On QA and DEV, Publication-Galleys is accessible. On PROD it is not. A post made by my colleague provides details and error log entry: Error viewing galley for a published article . The PDF is accessible on the issue and article pages of both our DEV and QA instances, but not on PROD. There is simply no PDF icon on PROD on either the article or issue pages.

This makes me think that an editorial action was taken on our PROD instance which somehow messed up access to the PDF. Can anyone suggest what an editor might have done to delete or render a PDF inaccessible and make it impossible to add a new galley? Or can someone suggest what I might look for on either the filesystem or in the database to figure out what may have happened?

many thanks