@MisterI 

Troubleshooting wireless ping latency is very challenging and requires physical presence along with proper equipments. I will provide some quick insight which might help explain the latency. However, I recommend searching the web for more information.

2.4GHz uses 11 channels whereas 5GHz uses 23 channels. Additionally, 5GHz is less crowded. Whereas, 2.4GHz frequency share devices with the like of garage door openers, microwaves and so on, and hence much more crowded. Crowded traffic tends to create interference, which possibly explain the spike. 5GHz and physical ethernet connection is less susceptible to interference, therefore, no ping latency spike.

If you are curious and want to better understand wireless networks around you, attempt the following:

• Review the wireless networks around your location.
• Separate which wireless network is 2.4GHz and 5GHz.
• Review all the devices that utilize the 2.4GHz nearby.

Good luck and do post/reply here if you found useful information.

@Godzilla 

Thanks for the quick answer.

I will try to change channels to see if it still happens.

I have seen some people disabling the N and using only the B/G but in this model I can't disable it.

I have other router which is much older that works on B/G that doesn't have this behavior, maybe it's something related to the N protocol?

@MisterI 

I'm not certain if it's the N protocol. New router has the ability to detect congestion and auto-switch to different channel. I don't have the C7 to review its wireless option. Additionally, there are devices that can interfere with 2.4GHz which are difficult to determine. There are mobile apps that can view WiFi networks and its channels, a good start to view wireless networks around your location.

If you simply just want to use the router, stop here. Ping latency spikes is tolerable if connection is stable and useable. I don't want to lead you down the rabbit hole 

If you are adventurous, review the C7 1750AC hardware and OpenWRT 19.07.3 compatibility. OpenWRT provides more features and more control over the router. The GUI does take time to adjust, but simple. OpenWRT and its firmware do requires some reading before proceeding. There is the possibility of bricking the router if not careful.

Backup plan, I recommend performing a router backup and tp-link firmware ready if needing to revert back to factory firmware. Additionally, have the used WiFi router handy incase of bricking the current router. Or if the old WiFi router is compatible with OpenWRT, try that first.

@Godzilla 
While its true that its usable in most cases, in my case, sadly isnt. I do videoconferences often and its annoying. Sometimes even disconnects me from the network cause of the lost packets in a short time.
 

The router is a few months old and it has warranty, so that solution would void the warrany .

I will reach TPLink to see if they can solve this. Thanks!