Missing /data/UID/ on CubicWeb instance - 404 - how do I solve it?

On a local developement instance of CubicWeb I get a 404 on

http://localhost:8080/data/4a587508844929a7393d7587696822d0/cubes.example.css

I've tried to run

cubicweb-ctl gen-static-datadir app

and there are some files in my uicache directory, but CubicWeb is not serving them, what can I do ? And how is the unique ID 4a587508844929a7393d7587696822d0 generated ? Is there a way to disable this ID to simplify URLs ?