There might be some configuration issue with a KNIME server. It takes multiple try to login. It prompts frequent error message that "Server ... cache update failed - loggin out." The second issue is that only one operation is allowed, such as deploying one KNIME workflow from client to server machine. It immediately logouts on its own. I take the two issues are related. Hopefully there is a way to resolve these issues.
a little late but just to make sure: Is this still an issue for you? Does the logout also happen after execution of a workflow?