OJS 3.0.2 pdf galleys not opening or downloading (after migration to new hosting company)

Having resolved an initial Http 500 error, I can now see and navigate the OJS pages. However, when I click on an article pdf I get " error occurred while loading the PDF" with the additional information “PDF.js v1.5.188 (build: 0e2d50f) Message: stream must have data”

If I download the pdf, I get an empty html file. I tried changing the file using the change file option in the production, but I get an http error at the end of the upload.

The error log shows:

22-Jan-2019 22:20:42 Europe/London] PHP Fatal error: Call to a member function getFileId() on null in /home/++++/public_html/ojs/lib/pkp/classes/submission/PKPSubmissionFileDAO.inc.php on line 1037
[22-Jan-2019 22:53:20 Europe/London] FileApiHandler: File /home2/+++++/ojsfiles/journals/1//articles/62/submission/proof/62-1-118-1-10-20190110.pdf does not exist or is not readable!
[22-Jan-2019 22:53:20 Europe/London] ojs2: 500 Internal Server Error
[22-Jan-2019 22:54:19 Europe/London] PHP Fatal error: Call to a member function getFileId() on null in /home/+++++/public_html/ojs/lib/pkp/classes/submission/PKPSubmissionFileDAO.inc.php on line 1037

Any clues as to what I should be looking at? The // in the pdf address looks odd!

Have you checked that the file name is correct?
The name is reassembled - in particular the ‘1’ between ‘62’ and ‘118’ is derived from a lookup on the ‘genres’ table and could be wrong; if so see Table 'genres' : Upgrade from 2.4.8.2 with MySQL 5.5.62 to 3.1.1.4 with MariaDB 10.1.37