Battery optimizers allow mobile devices to extend their batteries but at the expense of performance, notifications and even shutting down background services on your child's device. Boomerang in Child Mode needs to run as a background service and can get turned off by these very aggressive battery optimizers.
Sony uses it's optimizer named "Stamina mode" and it will break all background processes.
Never use Stamina mode if you want your phone to do something useful when you are not actively using it.
Try to make your app not battery optimized in Phone settings > Battery > Three dots in the top right corner > Battery optimisation > Apps > your app.
Tips from https://dontkillmyapp.com/sony