You are backing up any data to a local drive or a network share of any type. Backup schedule is other than "Always incremental". Always incremental archives are not affected by this issue as this backup scheme produces archives of another type.
At some point when you already have a full backup and create subsequent backups, the process starts failing or producing a warning: "The archive is invalid or its type is unsupported."
Issue can also happen when trying to delete the backup.