The filter values are based on property values that are read by the Tweakwise app. That means that you can always check strange values that appear in your filter within Tweakwise.
First, check which attribute is used in the filter template. You can do this by navigating to Filtering > Filter templates.
Open the template that displays the strange values. Below the name of the filter, you see which attributes are used in the filter.
3. Next, navigate to Catalog > Attributes and open the attribute on which the filter is based. Then click the Value distribution tab and click Table. You'll see all the values in the attribute in the table. The table will also display the strange values.
If you want to edit these values, there are two options:
Edit them in the feed;
Create a derived attribute based on this attribute.