Excluding nulls affecting calculated field x axis

I am looking at interactions leading up to a product sales. I have a calculated field for the x axis which says whether ‘email’, ‘crm’ or’ ‘email and crm’ channels were used into the lead of up to the sale. this is a bar graph which counts distinct product sales on the y axis. I have added a group by condition to split each of the channel options by scrum of the interaction which is attributed to the product sale. I used a calculated field for this which reads as ‘ifelse({INT_SELECTION} = 1, SCRUM, null)’. There are inevitably some nulls for where the scrum of a non attributed interaction is picked up. My issue is when I select the visual to ‘Exclude null’ - this results in nulls being removed but also my entire ‘email and crm’ column on the x axis which contained data from other scrums. Any idea why this could be?