Working on one backup and recovery control i get than sf database is in recovery model Simple. This is not the recommended method preconized for BackUps to prevent damages.
"Important Simple Recovery is not an appropriate choice for production systems where loss of recent changes is unacceptable.
using Simple Recovery, the backup interval should be long enough to
keep the backup overhead from affecting production work, yet short
enough to prevent the loss of significant amounts of data."
Could suggest you
ALTER DATABASE Sitefinity SET RECOVERY FULL