Do you have a battery saving app? This could be the origin of the issue. As Any.do continues running syncing processes to make sure your tasks are up to date, the battery saving app sees Any.do running in the background it and shuts it down. Then, Any.do restarts and this creates a cycle of shutting down and restarting the application, leading to extra battery consumption. If you have a battery saving app, please go into its settings and mark Any.do as an exception.