Pro-Forms CSS not rendering with 'External File' CSS rendering

Using BricksForge version: 3.1.8.7

My pro form element is not loading the css when generated on the frontend when I have the Bricks CSS rendering method set to external files. This fixes instantly when I change to inline CSS rendering, but don’t want to be forced to use inline just for this one element. I have recreated the issue on a brand new simple pro form with no attached scripts etc.