GIS Dashboard serial chart not showing correctly when something other than date is used as the category field

[SB_GIS_user]

Hello, I am making a serial chart in a GIS dashboard. When I select "date" for the category, my data are stacked nicely by date, with multiple points from the same date showing on the same value on the x axis:

However, when I use "river mile" as the category on the x axis, I have many values at the same river mile, but instead of stacking them on top of each other like a typical x/y graph, the same river mile value shows up multiple times on the x axis. I check and river mile is type long, not text so it should be recognized as numeric.

Any help is appreciated.