Uneven Gradient

I have a layer that is a blue gradient (to appear as underwater). The gradient appears as a series of individual colour rings rather than one smooth transition. It looks the same in GL and Render view, and is even more pronounced when I export the scene as a render.

I use Harmony Advanved on a top spec iMac.

Does anyone know what I am doing wrong?

No such linear gradient issues here, using radial works as usual.
Can you provide a download link of your project file ?