Hi Kreuters,
I hope you are doing well today! What version of LabVIEW are you using? One of the issues which might be causing this is that in the polymorphic Waveform Peak Detect VI, the "one channel instance" creates a new uninitialized "State Info" cluster for each call. When making multiple calls to the VI, this cluster should be passed from the previous run. Instead, the VI incorrectly creates a new uninitialized cluster. To pass the previous cluster, replace the Waveform Peak Detect one channel instance (called Waveform Peak Detection for 1 Chan VI) with the attached Fixed Waveform Peak Detection for 1 Chan VI.
If this doesn't solve the issue, be sure to post a snapshot of your code and let us know what version of LabVIEW you are using. And, giving some information about the code always helps. Have a great day!