that may not be the final solution, just an workaround.
we're still working on it --- to identify the root cause and completely fix it.
Can you provide a test case which can 100% reproduce the issue?
I have tried to reproduce the issue on our lab but not succeeded yet.
backup size is about 30M, backup to ithemes's own "BackupBuddy Stash".
use multipart uploads, max 15M every time. but succeeded without any issue.
this is what I thought will trigger the issue, but backup succeeded.
not tested with dropbox, S3 etc.