I haven't had a chance to read the article yet, but irns are a very unique species. I hate the term bluffing, it implies that you need to call their bluff, which is NOT a good way to handle the bird. In my experience, a sudden change like this usually has to do wi fear. The fear doesn't have to make sense to you to be real. Did something in the house just change? A new piece of furniture, new glasses on someone, new cage, new toy, new family member, change in routine? Did someone become too forceful with the bird recently, breaking his trust somehow?
It could be hormones also, though at his age I would have expected the issue to arise last year rather than this. Is someone snuggling him? Is his diet high fat? Is he not getting enough sleep?
I will read that article soon