A user has a filter variable in a document created from the Data Sources tree via + > Filter > New. When you update the data set with one that is missing a variable used in one of its conditions, it breaks and cannot be edited. In Properties, it states "A filter term is undefined", and when you try to open the filter definitions, this message appears: "This filter is too complicated to be edited here. It must be edited in Q." Users should be able to fix this in Displayr.