Using CODESYS V3.5 SP 2 and
CODESYS Control for Raspberry Pi SL version 3.5.15.30
Together with a DNS/DHCP Server made with another Pi
I get the following error in UaExpert when connected with a laptop.

17:41:43.393 | Server Node | OPCUAServer@harmonia-05 | Endpoint: 'opc.tcp://harmonia-05:4840'
17:41:43.393 | Server Node | OPCUAServer@harmonia-05 | Security policy: 'http://opcfoundation.org/UA/SecurityPolicy#None'
17:41:43.393 | Server Node | OPCUAServer@harmonia-05 | ApplicationUri: 'urn:harmonia-05:3S%20-%20Smart%20Software%20Solutions%20GmbH:CODESYS%20Control%20for%20Raspberry%20Pi%20SL:OPCUA:Server'
17:41:43.393 | Server Node | OPCUAServer@harmonia-05 | Used UserTokenType: Anonymous
17:41:43.393 | Server Node | OPCUAServer@harmonia-05 | The server returned no certificate, all certificate checks will be skipped.
17:41:45.685 | Server Node | OPCUAServer@harmonia-05 | Error 'BadHostUnknown' was returned during OpenSecureChannel
17:41:45.686 | Server Node | OPCUAServer@harmonia-05 | Connection status of server 'OPCUAServer@harmonia-05' changed to 'Disconnected'.

With another computer not a laptop I get the following
14:15:20.050 | Server Node | OPCUAServer@harmonia-05 | Connection status of server 'OPCUAServer@harmonia-05' changed to 'NewSessionCreated'.
14:15:20.051 | Server Node | OPCUAServer@harmonia-05 | Namespace table changed, mapping old to new namespace indices
14:15:20.051 | Server Node | OPCUAServer@harmonia-05 | Connection status of server 'OPCUAServer@harmonia-05' changed to 'Connected'.

I can add that I can ping harmonia-05 and I can also in a browser see http://hamonia-05:8080/webvisu

What the heck is wrong?