It's possible that the folder in question has the Versioning feature disabled. To view/change this setting navigate to the folder within the web application and access Advanced Folder Settings within the More Options menu beside the Folder Name.
I have a user who has uploaded PDF's into a folder on the 14.1.19, when she went to that folder today the files had reverted to the 31.10.18 and the previous versions from the 14.1.19 are not in the list!! this is a major problem as we are not sure if this is happening elsewhere in the citrix folders. She has saved these files elsewhere because we suspected this has been happening before