UPnP is used Syncrify/SynaMan to automatically configure network firewalls. This technology, however, is not considered secure and therefore, will be removed from Syncrify as well as SynaMan in future releases.
UPnP is a protocol that is designed to automatically open ports into a firewall by a program running inside your LAN. Since no human interaction is required to configure firewalls through UPnP, many pundits on the Internet consider it insecure as any malicious program could use it to change firewall settings.
Future versions of Syncrify as well as SynaMan will remove support for UPnP completely. Therefore, it is recommended you disable the use of this feature and configure your firewall manually.
Search security issues with upnp on Google to learn more about it.