Large file upload to SharePoint with slice and upload

We are trying to upload larg file to sharepoint online via provider hosted app mvc 5 with app only permission with below csom pnp guidance. It does upload file but makes file size to 0 byteswhen download so files looks corrupted.

There is no exception/issue while uploading so not sure what is wrong.

https://github.com/SharePoint/PnP/tree/master/Samples/Core.LargeFileUpload

if we use same code in console app it works just fine. Is anyone has experience in uploading large files to sharepoint via mvc provider hosted app(app only/user&app only permission)