@Klinge - It appears that your problem isn’t the same. @Sachse had two instances of the Magic Mirror framework running at the same time. You probably don’t have that problem.
The DWD site appears to be up and is hosting a json file. So let’s start at the beginning. Please post the relevant portion of your config.js file. We don’t need everything, just the part that configures the MMM-DWD-Pollen module. That will let us try and replicate your problem. Be sure to use the Markdown features when you post your code snippet!