Backup creation task hangs or fails when there is a domain with huge amount of files: Repository error: Archive error: unable to pack

Applicable to:

Backups creation finishes with the following warning in Tools & Settings > Backup Manager:

PLESK_WARN: Warning: domain "example.com"
Cannot dump domain hosting content [Repository error: Archiver error: unable to pack C:/Inetpub/vhosts\example.com. Archive creation failed. See logged errors for more information]

OR

PLESK_WARN: Warning: domain "example.com"
[4332da76-d5bd-4322-b8bf-43001218e6b7]: Unable to check existence of the file C:\Inetpub\vhosts\example.com\httpdocs\subdomain.com\domain_Data\DomainJSON\example.com.json. The file will not be archived. [:0]
A domain with few million files exists on the server. For example:

PS Get-ChildItem -Recurse $env:plesk_vhosts\example.com | Measure | Select Count | Format-List
Count : 12235020

Product issue:

#PPPM-9549 "Backing up of the subscription that has a large number of files no longer finishes with the warning."
Fixed in:
- Plesk Obsidian 04 June 2019 (fixed as PPP-39179, Windows)

Please consider updating your server:

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

temporary solution

Until the bug is fixed, apply the following custom fix:

Connect to the server via RDP
Download the custom fix:

PS [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
Invoke-WebRequest -URI https://support.plesk.com/hc/en-us/article_attachments/360019028453/customfix.zip -OutFile customfix.zip
Unpack the patched plesk_agent_manager.exe file:

PS Add-Type -Assembly "System.IO.Compression.FileSystem"
[System.IO.Compression.ZipFile]::ExtractToDirectory(($pwd).path + "\customfix.zip", ($pwd).path)
Backup the %plesk_bin%plesk_agent_manager.exe and %plesk_bin%pmmarchiver.dll files and replace it with the patched version:

PS Move-Item $env:plesk_bin\plesk_agent_manager.exe $env:plesk_bin\plesk_agent_manager.exe.bkp ; Move-Item $env:plesk_bin\pmmarchiver.dll $env:plesk_bin\pmmarchiver.dll_bkp
Place patched versions of the files:

PS Move-Item .\plesk_agent_manager.exe $env:plesk_bin\plesk_agent_manager.exe ; Move-Item .\pmmarchiver.dll $env:plesk_bin\pmmarchiver.dll
Proceed with the backup