Backup keeps storing old files

Hello, I set the configuration to store backup for last two days and 1st + 15th of each month. But sometime I see some servers doesn't delete the old backups for some reason. (Attached a screenshot) Again in some cases, some servers sudenly stops generating backups. Both of the issues are strange as if the backup stops, it will increase the chance of data lose. On the other case if it keeps storing backup the server will be full. Hopefully I can get a resolution here. NB: I store backups remotely. These issues aren't related to a single server, it happens suddenly on a specific server. If I run backup manally, it works though.