Is my beetle go hibernation?

It could be that the prevailing conditions in the terrarium are suboptimal for the beetle. For instance, you should check the ambient temperature and humidity and match these with the requirements for the particular species of atlas beetles in question. It could be that the terrarium is too cold and a light bulb emitting incandescent light is fine. They also tend to hide in crevices if its hot in order to stay cooler. It could also be possible that the beetles are in a state of inactivity due to being engorged with food.