If I don't use the product for a long time, the power sometimes goes off. Is my product broken?

No, it's not broken.
This product comes with an auto power off function, which is enabled as the default setting. The power turns off automatically when there is no signal input, output or operation for 20 minutes.
To turn on the power once the product has turned off automatically, press the power button again.
To disable the auto power off function, go to [Settings menu] > [System Settings] > [Auto Power Off] and select [Disable].