I'm trying to use terrain paints for the first time since the update, but they aren't appearing. I'm not even getting a radius for the brush, just the brush icon itself. Terrain tools work just fine, it's just the paint and erasing.

Terrain painting works for me. Even the custom terrain paints still work. But painting the slopes of raised ground can't be done, at least by me. You can paint the tops (if they are rounded) and around the bottom, but I can't get anything to stick to sides of my raised ground. And yes, the radius wasn't there on the slopes. I thought it had just got away from me somehow, but it just doesn't appear if painting that part of the ground is blocked. Maybe a patch will fix it eventually? Maybe I'm doing it wrong too?

When they have announced terrain tools they said you won't be able to use terrain paint on high slopes and such, so it's not a bug, it's a restriction..
they did however made it so each world has it's own terrain color for the deep slopes to fit with the world environment..

OP, check here maybe
https://answers.ea.com/t5/Bug-Repor...ps/td-p/7188917