Chatbot responds with empty output or blank characters

Hi everyone,
I currently have about 30 different intents defined in my model and the problem is that I cannot call various intents. That means if I enter a utterance during testing the chatbot that is stored with the respective intent, the chatbot generates an empty output or simply returns a blank character as a response (see screenshot) and does not return the response that I have defined for the respective intent.

Does anyone know exactly where the problem is and how it could be solved?

Thanks in advance and best regards,
Marcel