My new Files are disappearing after the upload

<%- if @topic_view.topic.tags.present? %>
<%= t 'js.tagging.tags' %>: <%- @topic_view.topic.tags.each do |t| %> <%= t %> <%- end %>
<% end %>

Hi,

We are using Silverstripe 4.3. When I upload a file (PDF) it is appearing in the CMS, however, if I assign any permission levels to my file it is automatically deleting by itself when I login to the frontend after uploading and assigning the file permissions.

Please Advise.

Thank you