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

Hello schumaku Nivedita BasuKhodanapur 

The hardware replacement of the device has been completed, however, the problem still exists on the newly replaced device, which means that the cause of the problem can be basically ruled out as hardware.

Previously, based on case number 48171868, the Chinese tech support had escalated the case to the US R&D at my request, and the feedback was that there was a hardware problem, and that's why the device was replaced, which is obviously wrong, so we should correct this mistake, but I'm not sure how to contact the US development team.
At present, the Chinese technical support think they can't reproduce this problem in the lab environment, insisting that it is my network environment, but can't tell me the specific reason, according to the test will be set to WAN port 2 (1G) when this problem can be solved, which means that the WAN port 1 (2.5G) and port 2 (1G) different configurations is the key to solving the problem.
The other difference between the test environments is that they are using the R7000P uplink device, and I am using the R7000.
So can someone please help me to solve this problem completely, thanks.