The assignee/candidateGroup filter behaves differently depending on the whether the view is `UserTask` or any of the other possibilities.
For any other than `UserTask` the filter includes the whole process instance where any userTask is assigned to a particular assignee/candidateGroup, for multiple assignee/candidateGroup filters this also means mutually exclusive filters like `assignee is demo and assignee is not demo` yield results when there is at least one userTask instance of the process instance matching one of these criteria. For `UserTask` views however the filtered result only includes the particular userTasks that satisfy all of the defined assignee/candidateGroup filters at once, thus mutually exclusive filters will not yield any results there.
The behavior of the filter for userTasks is desired as it makes it possible to pin down a report to only consider userTask instances assigned to a particular assignee/candidateGroup. For the other view reports the filters behavior is consistent with how other filters operate (on the level of a process instance) but it's not that obvious and needs clarification in the userguide at least.
- the described behavior of the assignee/candidateGroupFilter is described in the user-guide https://docs.camunda.org/optimize/develop/user-guide/process/filter/#assignee-and-candidate-group-filters