FTP backup is created incorrectly if several APS use the same database: boost::filesystem::file_size: No such file or directory

Applicable to:

Full backups are set to be stored on FTP storage in Plesk > Tools & Settings > Backup Manager;
There are backups in local storage in Plesk > Tools & Settings > Backup Manager;
There are backup files left in /var/www/psa/dumps/clients;
The following error can be found in/usr/local/psa/PMM/logs/backup-<datetime>/backup.log:

CONFIG_TEXT: INFO: boost::filesystem::file_size: No such file or directory: "/usr/local/psa/PMM/tmp/pmm-de-tmp-repo-6TJGee/clients/exaple.com/domains/example.com/databases/example/backup-pv22s37_1811151802.tgz"
[2018-11-15 22:00:37.381|29034] INFO: pmm-ras finished. Exit code: 1

Product issue:

#PPPM-9656 "Support issue PPPM-9656"
Fixed in:
- Plesk Obsidian (RC1 18.0.15 as #PPP-39525) 04 June 2019 (Linux)

Please consider updating your server:

If update is not possible for some reason you may try the following

temporary solution

For workaround implement the custom fix:

Log in via SSH;
Backup /usr/local/psa/PMM/agents/shared/Storage/Storage.pm file:

# cp /usr/local/psa/PMM/agents/shared/Storage/Storage.pm{,.bkp}
Download the custom fix and unpack it to /usr/local/psa/PMM/agents/shared/Storage/ directory:

# wget https://support.plesk.com/hc/en-us/article_attachments/360019382613/Storage-PP-17.5.tgz
# tar -xzf ./Storage-PP-17.5.tgz -C /usr/local/psa/PMM/agents/shared/Storage/