Issues with Calendar Grouping with numbers


I have been asked to provide a quarterly calendar view that shows all the projects being worked on in the upcoming quarter. They specifically asked to see all the projects grouped by their Business Priority. In our main sheet, we attribute a value from 0 through 4 for priorities.

In the calendar app, everything is grouped correctly, however the 0 (highest in our case) priorities are categorized as "No Category" and ending up at the bottom of the list, which is defeating the purpose of calling them out as a high priority. Any advice why this is occurring?

I figured I could make a helper column in the data that looks at the Business Priority column and if there's a 0, I could make it a different character and then the rest would just be the number as is.