@shrey there's some cases where the backup code forgets about older backups. For example, if you switch backup providers (even temporarily). We are trying to improve the whole situation in 9.0 . For a start, with multiple providers, we can track/cleanup more accurately.
BTW, if you paste the filename of the backup in your Eventlog, does it find it there? I will look into making this more clearer i.e what is getting deleted and why not getting deleted.