Daniel, backup files were not corrupted in my case, just the postgres database was shut down uncleanly.
I don’t think your backups are corrupted, they just need to be run on the same major version of postgres as they were created on.
Do you by any chance use the Discourse image from Scaleway’s ImageHub? In which case I strongly recommend you not to but create a clean Ubuntu 16.04 VPS and follow the official readme. Also, don’t forget to choose the Docker kernel in advanced settings.