See here for introductory information about manufacturer specific issues...
Sony devices have a feature called 'STAMINA Mode'. This feature will break all background processes if enabled.
- Settings > Power Management > STAMINA Mode > Make sure that STAMINA Mode is deactivated.
You can also configure your device to enable STAMINA Mode once you reach a certain battery level. Make sure you disable this as well as we don't want STAMINA Mode to get re-enabled.