This might be due to the fact you are using external IP
You need to allow external IP + port to be used from qpack server
for ex: http://[external  ip]:[Port]/qpack/DocGen/tblFilter.aspx?FID=[filter id]&VID=[version ID] should get results the same as  http://localhost/qpack/DocGen/tblFilter.aspx?FID=[filter id]&VID=[version id] in your Qpack server.