This might be because you have a memory cleaner / anti virus / booster app.
These might be killing drupe and preventing it from running in the background, hence the disappearance of the dots. If you do have such an app installed, try to check its configurations.
Unfortunately, this might also be happening without having such an app - some devices have in-built memory cleaners that automatically stop apps that run in the background. While this only happens on a small number of smartphones, we are learning this issue and trying to figure out ways to prevent this.