Yeelight always offline

Hello. I have two colour yeelights and an Alexa. I had the lights for ages and they both worked fine. occasionally I had to power recycle when they show as offline but that always worked. Now one of the lights doesn’t respond to Alexa and always shows as offline within the app. I have done Power recycles and nothing works. I am at a loss for what to do as it simply doesn’t show up as online. Nothing is wrong with the router; the other light is always okay. Wondering what to do. I can switch it on at the plug but can’t do anything else with it. It’s just standard bright white light.