Paintbrush/other similar tools only paint on initial click

My tool has been working fine for ages and then suddently it only seems to paint on the initial click of the tool. Dragging my mouse does nothing. I only get the initial dot from the click.

I checked the settings and spacing is all the way at 1%. None of the other settings are active. I tried turning spacing off, but then the brush seems to apply its own spacing depending on the speed of my mouse stroke. Any ideas?