Filters only work on part of the value within the dropdown list

Hi Team,
Appreciate if anyone looking at this question in advance!
I created a dashboard that contains multiple filters with correspondent parameters. I created filters one by one, e.g: Platform filter, country filter, start Date filter, Program filter etc.

Most of the filters are in string type with multiple dropdown selection. However, some of the filters work well and the others fail to filter the correct data.
For example, there is a filter contains A, B, and NULL. If I uncheck the NULL value then the NULL value disappear in the dashboard, but when I uncheck B, B still showing on the dashboard, which means somehow the filter only works partially.

Here is my filter setting process:

  1. Create a parameter for the measure in the String type with multiple value selection and leave the default value blank.
  2. Add the parameter to the control, select multi-select Dropdown, Link the value to dataset field.
  3. Add a filter and select custom filter as filter type, set Equals filter condition and checked the “Use parameters” box, and eventually select the parameter just created.

Can you show me screen shots of these errors?

Are you sure these filters are across all visuals and that the filters are linked to that exact field?