Crashs & restart independently

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My UMI Z restarts itself from time to time. E.g. when i try to start the camera, or when i start an app (last time i was surfing on my facebook page, i wanted to comment on a post, but first of all i wanted to change the language of the
keyboard on swiftkey (keyboard app). Suddenly The screen goes black, the phone turns off and it restarts itself.

Serious problem. UMI please fix this.