BackWPup Error

We have several websites using BackWPup and we typically do daily and weekly backups. We continue to get the following errors:

WARNING: There was an unknown error when uploading the file.
ERROR: Uploaded file size and local file size don’t match.
ERROR: Step aborted: too many attempts!
ERROR: Job has ended with errors in 9 seconds. You must resolve the errors for correct execution.

WARNING: Could not look up the file session.
WARNING: The file could not be uploaded.
ERROR: Uploaded file size and local file size don’t match.
ERROR: Job has ended with errors in 113 seconds. You must resolve the errors for correct execution.

These errors only occur sometimes, and sometimes the backup runs smoothly.

Please let me know if there is additional information you will need to help me fix these errors. Thank you.