The situation:
Downloading a 2.1 GB file with b2 download-file-by-name (or b2 sync) crashes midway with TruncatedOutput: only 1495314753 of 2121389892 bytes read. Small files download fine; large downloads crash anywhere from 1.4 to 2.0 GB. When a network hiccup interrupted the data stream mid-download, the CLI failed the whole download instead of retrying the interrupted part.
What actually fixes it (verified in the thread):
This was a bug in the B2 CLI, not your network: it did not retry when the data stream was interrupted mid-download. Maintainer mjurbanski-reef confirmed B2 CLI 4.1.0 fixes it by properly retrying mid-stream errors, so it now works even when the network is congested. Upgrade the CLI to 4.1.0 or later and re-run the download; the reporter verified the fix closed the 90-comment issue.