SFTP Policy does not transfer the entire file. The file is transferred in increments - For example - 1st file is 32KB, 2nd is 64KB, 3rd is 128KB and so forth until the final file is 650KB (the size of the file being uploaded in this use-case). Or only 32 KB of the 650 KB file is transferred at a time.
Environment
API Gateway
Resolution
Uncheck the option "Forward SFTP partial uploads to policy" in the listen ports properties under the 'PUT' method.