Shared Link Recipient Can No Longer Upload

We haven't used this feature for a couple of months so not sure what has happened in between.

We select a folder to be shared, we create the shared link then copy the link and email it to a non Box account holder. Normally they can access the folder, click on an upload button then select their files to upload.

Yesterday we went through he same process for another folder and another user. They could access the folder without an issue, however, there is no option (button) for them to click, select a file and upload. 

Can someone please let me know if the functionality has changed over the last couple of months or is this a current system error, or some other reason?

Thank you.