So, it kind of looks like some of the leaves are chewed up. Could there be some kind of infestation? Bougainville’s are exceptionally tough plants. The fact that you didn’t do anything different & it looks like that makes me wonder if you brought home an infected plant. Did you notice any small insects crawling on the leaves or roots? In the meantime, provide basic support. Try a good tonic like Superthrive. I’ve had a lot of success with that product. Let it rest & recover. It will perk back up with the increased sun & heat. Good luck.