Abnormal delay in pinging the gateway ip through WAN 2.5G port.

If you bought it from Amazon US you have contract with Amazon US.

Assuming the device was properly registered, it's registered with Netgear as a US device, in a US location. Device return goes on your expenses, and exchange shipment can go only to an US address, they won't ship it abroad.

Where you live or where you have exported the device to is your own personal choice. 

One additional reason is that you have exported an FCC regulatory device to abroad, FCC regulations (not Netgear!) don't permit to change the radio config to other regulations, so you are operating a device illegal to operate in China mainland.

FMI https://en.wikipedia.org/wiki/List_of_WLAN_channels 

I doubt you can order a US device from Amazon China. Sure, Amazon has (or had) a very poor customer information policy and does not correctly inform their customers, they often allow shipping ways beyond of what is allowed. Yes, Amazon e.g. US does typically not care if the customer is ordering for shipping to an address abroad, so Amazon does (or did) often allow to ship FCC regulatory devices to addresses abroad, handing over the full risk and responsibility for the import to the receiver. It does not matter if Amazon does handle the shipping to abroad: You are the buyer, and become the importer for the destination address. 

By far not a lawyer on trading and importing, however: In brief, this is what applies for self-importing radio equipment into Switzerland (and more generic into Europe). First hurdle will be the lack of CE mark on the FCC devices 8-)