Line thickness and scale... what happened?

[AdrianWelsh]

This has to be a dumb question but I can't figure it out. I have lines on a map at 1 point thick (ArcGIS Pro 2.4.1). Pic:

(you can see the scale at roughly 1:9,000)

But when I zoom in, they don't change based on scale anymore. It kind of acts like layout view versus data view:

(scale is 1:3,700)

And zoomed again:

(scale 1:1,500)

I know it has to be a setting in Pro to make my lines scalabe but I can't find it. I feel like this is a new "enhancement" since I don't recall old maps having this behavior.

Please help, haha!

[KoryKramer · Accepted solution]

Check the map's reference scale: 

Map reference scales—Properties of maps | ArcGIS Desktop 

[AdrianWelsh]

Ah, brilliant, thanks Kory Kramer! 

I will do that from now on when I see this.