Access denied to upload discussion file (Copyediting, Production stages)

Hi,

We use the OJS Version 3.2.1-4. When someone (author or editor) wants to upload more files, e.g., with similar but not the same name, the system warns us: „Possible Duplication or Revision Detected”. We select „This is not a revision of an existing file”. Despite this, sometimes it doesn’t allow us to upload more files; it writes „Access denied”. The same happens randomly we try to upload more than one file both in Copyediting and Production phases.
Unfortunately, this doesn’t trigger any error messages in the server logs or the browser console, so it is hard to troubleshoot.
We please your kind help in this case.
Access_denied

Many thanks,

Nrado