I just lost a bird who looked quite similar. She was really healthy appearing up until about 2 weeks before and then suddenly looked off. She was 6 years old and still laying. No abdominal bloat, no ascites, but she was thin (which I only discovered when she looked off, she was not a bird that liked to be handled). She just deteriorated. Necropsy showed she had reproductive cancer and her liver was in really bad shape. She even had a small egg in her system. I'm just sharing because symptoms can vary, and it can be really hard to know what's going on for sure until necropsy. I've lost birds to cancer that were very bloated, and a few that were not, they just got very thin. They are really, really good at hiding symptoms until things are very advanced, and feather fluff can hide a lot. It's actually important to pick them up regularly and check body condition, since you can't always see it easily. I did not handle this one a lot because she was so awful about it.
I agree with all the others that it looks like a reproductive problem with your bird.
I agree with all the others that it looks like a reproductive problem with your bird.