UV Sculpt tools not working at all in 2.82.7? I'm fairly new to Blender and this is my first unwrapping here.
I'd like to manually pull and pinch my UVs to reduce the stretch of the projected UVs, however, UV sculpt tools do absolutely nothing.

Here's a short clip illustrating my issue: 
https://i.imgur.com/XQLBXBU.gifv

(i know those UVs aren't pretty, but hey, I'll get there)

What is preventing the tool from having any effect on the mesh? I remember trying it out in the beginning of the process and it seemed to work, but now it suddenly is defunct.

Thank you in advance.
Ok, it got solved through recreating all UVs from scratch again. I still have no idea what happened (probably a bug of sorts), but now it works. Sad that it made me lose a couple hours of work, though.