It is currently impossible to use the receiver within the groovy configuration, even though it is coded (although it is undocumented). The following groovy will cause the issue:

receiver("SOCKET_RECEIVER", ch.qos.logback.classic.net.server.ServerSocketReceiver)

Digging into the code, there is a typo in the addInfo call in ch.qos.logback.classic.gaffer.ConfigurationDelegate#receiver. It's referencing clazz.name, when it should be referencing aClass.name.