Yeelights appearing offline

I am away from home at the moment but i control my bulbs via cloud. Yesterday, one of them appeared offline. Today both of them appear offline. This happened before many times especially with alexa not being able to control them snd only solution to switch the electricity plug off then on. I am not sure but it seems they go to this “offline” not responding state after a lot of hours have passes without being used. Please fix.

What’s the product model and firmware version?