This error can happen if you redirect get's in an endless loop. So you redirect to a page that redirects you to your original page. So check your deeplink config if something like this can happen.
While Ronald's answer was probably the right answer after all, I decided to post the definitive, more concrete answer and solution to the problem as a separate answer. Thank you for your help, Ronald!
We found the solution for the error. Constant DeepLink.LoginLocation was populated with the domain name of the test node. That was not supposed to happen since we want to use the login page that is included in the resource folder of the deeplink module. After I cleaned the constant and restarted the node, the deeplink works fine and shows the login page correctly.