Internal Server Error When Uploading PDFs

Hi

I'm getting a similar error to https://forum.grabaperch.com/forum/12-17-2017-500-error-updating-a-page, however, this was working fine until we upgraded the site to Perch 3.

When I try to upload a PDF it comes back as an Internal Server Error.

Funny enough the PDF and page are getting uploaded / updated perfectly well, but if I view the assets the PDF thumbnail isn't displaying. As you can see, previous PDF uploads are so I don't know if this is connected?...

If I select a PDF where the thumbnail is displaying, it works perfectly, only when I select the thumbnail that isn't displaying I get the 500 error.

Template...

     <div class="col-xs-6 col-sm-4 col-md-3">
        <div class="text-center doc-thumb">
         <a href="<perch:content id="docFile" type="file" label="PDF Document" bucket="documents" />" target="_blank" class="equal-height">
          <img src="<perch:content id="docFile" replace=".pdf|-w150h150@2x.jpg" />" alt="<perch:content id="docTitle" type="text" size="xl" label="Document Title" />" class="client-logo">
         <br>
         <perch:content id="docTitle" />
          </a>
      </div>
    </div>

Diagnostics...

Perch: 3.1.1, PHP: 7.0.30, MySQL: mysqlnd 5.0.12-dev - 20150407 - $Id: b5c5906d452ec590732a93b051f3827e02749b83 $, with PDO
Server OS: Linux, cgi-fcgi
Installed apps: content (3.1.1), assets (3.1.1), categories (3.1.1), perch_forms (1.11)
App runtimes: <?php $apps_list = [ 'perch_forms', ];
PERCH_LOGINPATH: /cms
PERCH_PATH: /home/eoc/YWY3GABL/htdocs/perch/cms
PERCH_CORE: /home/eoc/YWY3GABL/htdocs/perch/cms/core
PERCH_RESFILEPATH: /home/eoc/YWY3GABL/htdocs/perch/cms/resources
Image manipulation: GD Imagick
PHP limits: Max upload 128M, Max POST 128M, Memory: 256M, Total max file upload: 128M
F1: 3b606135b33e6a102526838f4152a807
Resource folder writeable: Yes
HTTP_HOST: eocservices.co.uk
DOCUMENT_ROOT: /home/eoc/YWY3GABL/htdocs/perch/
REQUEST_URI: /cms/core/settings/diagnostics/
SCRIPT_NAME: /cms/core/settings/diagnostics/index.php

Debug...

Debug Message - Perch 3.1.1
[1] SELECT u.*, r.* FROM perch2_users u, perch2_user_roles r WHERE u.roleID=r.roleID AND u.userEnabled=1 AND u.userID=1 AND u.userHash='2f34eeda0c6c94374cd77ed96e3a6659' LIMIT 1
UPDATE perch2_users SET userHash='437237a7d91e1e1ab20623d8169c42af' WHERE userID='1'
[26] SELECT settingID, settingValue, userID FROM perch2_settings WHERE userID=1 OR userID=0 ORDER BY userID ASC
[7] SELECT itemValue FROM perch2_menu_items WHERE itemType='app'
[1] SELECT * FROM perch2_content_regions WHERE regionID=218 LIMIT 1
[1] SELECT * FROM perch2_pages WHERE pageID='32' LIMIT 1
Using template: /templates/content/documents.html
[1] SELECT * FROM perch2_content_items c WHERE c.regionID=218 AND c.itemRev=83 AND c.itemID=320 ORDER BY c.itemOrder ASC
Using template: /templates/content/documents.html
Form not posted or did not validate
[1] SELECT mi.*, p.privKey FROM perch2_menu_items mi LEFT JOIN perch2_user_privileges p ON mi.privID=p.privID WHERE mi.itemActive=1 AND mi.parentID=0 ORDER BY itemOrder ASC LIMIT 0, 1
[2] SELECT mi.*, p.privKey FROM perch2_menu_items mi LEFT JOIN perch2_user_privileges p ON mi.privID=p.privID WHERE mi.itemActive=1 AND mi.parentID=1 ORDER BY mi.itemOrder ASC
[1] SELECT itemTitle FROM perch2_menu_items WHERE itemType='app' AND itemValue='content' LIMIT 1
[1] SELECT mi.*, p.privKey FROM perch2_menu_items mi LEFT JOIN perch2_user_privileges p ON mi.privID=p.privID WHERE mi.itemActive=1 AND mi.parentID=0 ORDER BY itemOrder ASC LIMIT 1, 10
[2] SELECT mi.*, p.privKey FROM perch2_menu_items mi LEFT JOIN perch2_user_privileges p ON mi.privID=p.privID WHERE mi.itemActive=1 AND mi.parentID=2 ORDER BY mi.itemOrder ASC
File: /core/apps/content/modes/edit.form.post.php
[1] SELECT * FROM perch2_resources WHERE resourceID='600' LIMIT 1
Mode: edit.form
Queries: 14
Memory: 3.4822