UI CSV import failing file not found

We have a customized version of Pimcore. In the DataObjects we have an attribute mapping that requires being loaded via a CSV when we set up a new server. In our staging environment this feature works, however in our production environment it gives the following Exception:

Warning: file(/var/app/current/var/tmp/import_5f8989f00288b_original): failed to open stream: No such file or directory

when I ssh into the server I can see the file indeed exists. It seems to fail on line 111 in vendor/pimcore/pimcore/lib/Tool/Admin.php
The line is:
$sample .= implode(’’, array_slice(file($file), 0, 11));

From what I can tell this file exists and has proper permissions and is owned by the correct user.

Has anyone else seen this?