If your device is a low-power device (devices that use battery and various sensor devices), in order to ensure battery life, the low-power device will only display offline in the App after it is offline for more than 24 hours, so it is very likely that your device has already offline, but you don't know. You need to readd it.
If the device still has problems after re-configuration, we recommend that you reset the device to factory settings in the App and remove it, and then add it again;
Please check whether the distance between the device and the router (no more than 5 meters without separation, no more than 2 meters with walls, metal objects, etc.) is too far, causing loss of signal transmission. To solve this problem, it is recommended that you remove the device first, then reset the device to the network configuration state and perform network configuration again. Please keep the network signal good during the connection process.
Confirm whether your account is in the correct region. If the region is selected incorrectly, the cloud server registered by the device is far away from you, which will cause a great delay and cause control failure.