Certain PDF documents are uploaded but not others. Message: "File *.pdf could not be uploaded. Please try uploading it again."

I am trying to upload a specific PDF; I am in the cloud environment using Appian 19.4. I am getting message, "File transcript.pdf could not be uploaded. Please try uploading it again."  The PDF which uploaded successfully meetingminutes1.pdf is twice the size in kilobytes and has the same change permissions as transcript.pdf. I suspected it had to do with the Enabled Real-Time Virus Scanning but I checked /logs/audit/blocked_files.csv and it is empty.  

Are there any known causes for such a scenario? How can it be fixed?

In the screen shot provided I first tried to upload transcript.pdf and then I successfully uploaded meetingsminutes.pdf.

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