Note: This article has the reference to the issue with the fix available:
"Under specific circumstances, full backups were created instead of incremental ones in Plesk."
- Plesk Onyx Update 16 13 February 2017 (Linux)
Incremental backups for some domains show the size of the full backup. Or all incremental backups for a domain have the same size despite the fact nothing was changed on the server, thus, incremental backup size should be different.
This is an internal issue with ID #PPPM-5447 , which is planned to be fixed in future product updates.
As a workaround, apply the custom fix:
1. Download the custom fix attached and unpack it.
2. Save the original file:
# cp /usr/local/psa/PMM/agents/PleskX/PleskX.pm /usr/local/psa/PMM/agents/PleskX/PleskX.pm_backup
3. Place the unpacked