In case you have not used Sitecore Support Portal in a while, Sitecore made a change on where to upload the files needed in order to investigate a ticket.
This message can be seen in email notifications from Sitecore Support:
NOTICE:
Sitecore Support File Server available at ftpes://dl.sitecore.net/upload is scheduled for decommissioning on 01-Feb-2019.
Please use an alternative approach for exchanging files with Sitecore Support team via Sitecore Support Box Storage.
Additional information is available here: https://kb.sitecore.net/articles/862874
Basically if you wish to upload files larger than 10 MB to the Sitecore you will need to use the new option that is available to everyone Sitecore Support Box Storage.
After you login to Sitecore Support Portal its quite easy to find Sitecore Suport Box Storage:
As a limitation you cannot upload more than 3 files at once and each file not bigger than 1 GB.
You also have the possibility to mark the files to what ticket number it belongs to:
Compared with the old ftp option, now you have the option to remove yourself old files, and sort them too.
Sitecore Support Box Storage security:
1. Files uploaded via this dialog are accessible only to Sitecore Support engineers and are automatically cleaned up 90 days after the upload date.
2. Your colleagues are able to see the full list of files but cannot download them.
For more information, refer to the following article: https://kb.sitecore.net/articles/862874.
XtremDev - Sebastian Tecsi | Sitecore Blog 