Answer by DiegoSLTS

Make sure the object with MyCustomGameObject component is active. Make sure the MyCustomGameObject component is enabled. Make sure nothing removes that game object from the scene, or deactivates it or the component. Make sure Time.timeScale is not 0. A coroutine will only work with all that, deactivating or destroying a game object that started a coroutine will stop that coroutine at that moment, and if the objects was already deactivated the coroutine will run until the first return statement. Aslo, the WaitForSeconds return depends on the timeScale, if it's 0 the 1 second will never happen.