Difference in File Size

I have a pipeline that seems to be dropping bytes somewhere. In the Manager tab, we can view the file produced by a pipeline we’ve developed to capture logging data. The file size on the main File tab displays one number of bytes, but when the file preview is opened, a smaller number is displayed. The smaller number seems to be the actual number of bytes that are read by the pipeline on the next iteration. Can you tell me what is causing the discrepancy and how to get the full number of bytes read?

Thanks!