you dripped developer down the length of film! ok that's not it!

What intrigues me is that you have different densities in the bands but they are not least->most. Having done this once, if you'd didn't have enough developer in the tank I think you'd get a distinct line where the developer came to. Even if you sat the tank down uneveningly you'd get light at the top, dense at the bottom with varying bits in the middle. This assumes you're processing in a small tank? If you're using some sideways mounted roller device...

I'm more wondering a light leak somewhere. Do you bulk load your film? What are the film edges like, any fogging? Also check the inter neg gaps.