The Qlik Sense environment adds log lines every second to the C:\ProgramData\Qlik\Sense\Log\Repository\System\Systemname_Service_Repository.txt
The following error is logged every second:
Failed to post server node configuration to host 'hostname.lan' Command=Server node registration;Result=-2146233088;ResultText=Error: Exception when calling 'https://hostname.lan:4242/configuration/servernode/activate?xrfkey=ichbineinberlinR
Central Node is trying to send the configuration to a RIM node which already has the correct configuration.
Changing the log level on the Central node, the change to the additional RIM node is correctly picked up and shows the connection as set up properly.
Restart the Qlik services on the Central node.