If you set after call action "Auto log & upload", you can sometimes see many unsynchronized calls (1 day old). It can be caused by the absent required internet connection. Another typical reason is special Android's saving Doze mode or Standby. The Call Utils can't fight against these battery saving features because we don't want to exhaust your battery.
If you require immediate synchronization, simply visit their call's detail page. It will automatically trigger synchronization process.
Some issues may occur in the synchronization process. These may be some common cases like "waiting for internet connection" or "no valid subscription".
If an error occurs, it will be described below the last sync state. You can click the error message any you'll get error description (see the screenshots below), error from the Salesforce API or exception message which can help you. Post this detail message with explanation to your Salesforce administrator.