@reysu47 After couple experiments I found that it may be caused by some application on my iPad. After I disconnect my iPad from Wifi, the spikes disappeared. Don't know why but I rebooted my iPad and...

I use 2 Deco M9 plus as AP and recently found that there are periodical ping spikes every 10 seconds, which makes online gaming impossible. I also noticed that there are repeative error logs appeared...