OJS PDF not showing

Description of issue or problem I’m having:
Help desk is upgrading from to 3.x but progress is slow and a problem with displaying PDF in has arisen which I really need to solve. Previously published articles show normally when the PDF link is clicked but uploading files to the site frequently fails. However, when uploading succeeds and the article is published, clicking the PDF link shows a blank page and clicking the “View proof” link in the Editing page only shows the summary page for the article. Can anyone suggest a fix. The last time I asked for help here it was suggested I upgrade but then as now the upgrade was incomplete and I am looking for a fix to this OJS problem.

Steps I took leading up to the issue:
Helpdesk says there are many PHP errors in the logs and has not had time to address them and has rather devoted the time to fixing translation errors in the DB.

What I tried to resolve the issue:

Application Version - e.g., OJS 3.1.2:

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

To fully understand the problem, it is necessary to examine it in detail.
Or you need to share the php error logs with us here.

Even if you solve the problem today, I recommend you to upgrade to OJS 3.3 as soon as possible.
The problems you are experiencing may increase day by day.