Hi hci,
There have been several recent threads on this. This was reolved in 15.1.5 so if you're on an older firmware version you'll want to upgrade to it or beyond it. The latest version is 16.0.1 and you can download it here. However, there is an issue where CPU usage hits 100% that may cause this and this issue will be resolved in 16.1, an upcoming release. You can check out the related posts here and here.