Plugin version defined in plugin_pack.conf does not match to the version defined in plugin_upgrade_match.conf. In plugin_pack.conf the version was defined as "R80.20-GA", while in the file plugin_upgrade_match.conf the version was defined as "R80.20".
This issue happens when /opt/CPupgrade-tools-R80.20 directory exist on one machine and not on another. This directory will be created automatically when user ticked the option to receive the updates from DownloadCenter automatically.
plugin_pack.conf file will be updated automatically when device connected to the Internet and received the updates from DownloadCenter successfully.