Failed to restore a Full backup file (sftp)
The first log snippet you posted is from version Version: 18.104.22.168
Were all of your backups made using this build? It's been in deprecated status for about 4 years now and the issue seems to be strictly related to SFTP setup, Windows uses different wording for EOF error.
Did you use compression during the backup?
Can you open that file outside of our software by simply copying it from the storage?
What is the backup time difference between the data that can be restore and the data that can't be?