Word Application Scope - Export To PDF - Process freezes

Hi Experts

I have build a process that opens a Word document and converts it to PDF. It is all done by creating a Word Application Scope using the Export To PDF activity inside.

The job is scheduled to run automatically and in most cases everything works fine. However on some rare occasions the process freezes doing nothing. In the Event Viewer the following error is reported:

System.Runtime.InteropServices.COMException (0x800401E3): Operation unavailable (Exception from HRESULT: 0x800401E3 (MK_E_UNAVAILABLE))
at System.Runtime.InteropServices.Marshal.GetActiveObject(Guid& rclsid, IntPtr reserved, Object& ppunk)
at System.Runtime.InteropServices.Marshal.GetActiveObject(String progID)
at UiPath.Word.WordDocument…ctor(String documentPath, Boolean createNew)

I have noticed that Word is not closed properly after the PDF conversion. If I go into Task Manager there is a Word process running and if killing the process the job will continue.

Any ideas what is causing this?