Missing neck feathers

I need some advice. My male rainbow lorikeet has a couple of missing neck feathers. This has now been going on for almost a year. I give them plenty of fruit, fresh foods and tried a variety of supplements.

The literature I went through did not bring me any further - I seem to be covering all angles. The female has perfect feathers. Has anyone experienced a similar situation and knows how to resolve it? The bird seems in perfect health otherwise.