Pics of before. if you push on it, it will can, but it comes back to its happy place. Either position will be a wave no matter what. I have eliminated most of it with skim coating, but it looks like it was there from factory so I don't want it too perfect.

No judging my welds.

Sometimes things go smooth and other times I have to go over it multiple times to get it right. Good thing someone invented a grinder.
You can see when I made the cut it relieved it some? Who knows. I am learning there is nothing that can't be fixed with a welder hammer and some filler.