@InternetGuy 

Those are spike to the gateway.  We would first start by disconnecting all but one device and running the ping test again.  This will ensure that no other device is broadcasting enrounious data causing the spikes.  If you still see it with just the one device, switch devices to rull at the 1st test device.  If that resolves the issue then the ping spikes were caused by something on one of the client device and you will need to troubleshoot that.   If that does not resolve the concern we would recommend starting at the Frimware and updating that if it is needed. 

@Carl Thanks for the reply. The issue turned out to be the TP-Link AC1200 USB wireless reciever I have plugged in to my PC. Rebooting or putting the PC to sleep fixes the issue, but it just keeps coming back at random. You'd think TP-Link's hardware would play together nicer.

@InternetGuy 

Some thoughts:

-) Assuming you're connecting via Wifi, how is the wifi connection established?  802.11ac or something else?

-) Can you try using another wifi channel instead of your current one?

-) Do you have another accessible computer that you could use for testing?  If it has wifi, retry your tests to see if the problem occurs there as well.  You could also try plugging the USB receiver into that other computer (ensuring to remove/disable any other wireless gear that may be present) and re-running your test.

Hope this helps.

T.