Rings around Brush instead of being feathered.

[Jafaraway]

I'm new here. Been using gimp for a long time now and sometimes run into the problem I'm currently having. Sometimes when I use one of the standard feathered edge brushes in a transparent layer, the brush's edges are a bunch of concentric circles, instead of being nice and feathered. However if I use the same brush directly on the background, it does look nice and feathered. Is there a setting that fixes this? Or am I doing something wrong?

See attachment. Thank you to anyone who can help with this.

[Ofnuts]

This is banding, caused by a "slow" gradient where an identical change of values occur at the same time on neighboring pixels and your brain interprets it as a line.

In your case this is worsened by round-off errors and the quantization that happens because you are in a low precision image. If you change the image to high-precision (Image > Precision) (typically 32-bit FP, the other HP modes are rarely useful) and repaint, the result should be a lot  better as far as my tests go.  But the banding can reappear later, when you will export the image to a low-precision format (JPEG or 8bpc PNG). You can mitigate it using Filters > Noise > Spread. This stirs the pixels a bit and the "identical change of values" no longer occurs on a line so our brains don't perceive it.

[Jafaraway]

That worked! Thank you so so so much for that information. You're the best