Stylesheet changes not visible until I change permalinks

Hi guys
I’m currently working on a site which uses the storefront theme + a child theme i’ve created.

I’m becoming increasingly frustrated as none of my styling changes appear when I upload via SFTP. However, I have found that if I upload, and then change my permalinks from ‘post-name’ to ‘numeric’ > Save, and then change back to ‘post-name’ the new styles are then instantly visible.

Has anyone got any idea what might be causing my problem?
Thanks