Problem with Call Workflow Service node

Hello

When I add a Call Workflow Service node to my workflow I can configure the input and output ports. However, most of the times I enter the node configuration again, input and output definition has disappeared, getting the following error:

It seems not to be a problem of a specific called workflow, because it is happening always when I try to call local workflow services.

Any suggestion? I am using KNIME AP 5.4.1

Thank you very much for your help