@Kevin_Z 

good info in these posts re ipv6 but clearly since the 1.4.x firmware this has caused the latency is this being investigated please ?
 

really disappointed as the m5 had solved all my wifi issues up till this point as were really responsive, guess may have to look for alternative products if this issue can't be resolved 😦

@tobyw I have the Deco E4, same exact issue but disabling IPV6 doesn't change anything. It's a differen model, but I think there's a common explanation for this issue

@Daveomania 

Hello to anyone still following this thread -

I found another thread describing the same issues with a Deco M9 and a temporary solution which has been working for me. 

In my Deco App, I select any device that I don't want these latency spikes occuring on (In my case, this is every device on my network) and I disable the "Mesh Technology" in that device's settings. 

I believe this means that the device will not swap "seamlessly" (Yeah, right) between decos. 

So far, I have not had a latency spike on my devices since doing this. 

I haven't found a way to disable "Mesh Technology" globally, but it only takes a few minutes to disable this on each device in the list. 

Hope this might help. 

Here is the thread I found this in: https://community.tp-link.com/us/home/forum/topic/180030?page=2

@Daveomania Fantastic!!!, its work for me!!!, I have two deco M4.

@Daveomania has anyone found a solid solution to this? I am having major issues with my DECO M5 mesh network. 
I'm running a total of 7 decos within a pretty large area, about 8000sqf, both indoors and outdoors. 

I've tried disabling mesh for devices, but still the same. When there is no load the ping is around 4-20ms and time out about 1 in 50 pings. 
But as soon as I download something the pings rockets to 200-2500ms and time out in about 15 in 50 pings. 

Has anyone found a solid solution for the ping and time out issues? 

@AndreasSwe I never managed to fix this issue, I'm just living with it now and I'm looking for a replacement sometime in the future. No Tp-link this time though.. I used to like their products but the fact that they are ignoring problems like these is a deal breaker for me.

@AndreasSwe 

I have tried to be patient while waiting for more help from TP-Link with this problem since I have had good experiences with their products over Linksys or D-Link in the past, but it seems as though they have decided to ignore this issue now.

I swapped my deco m5 mesh system for a similarly priced product from MeshForce (MeshForce M3) and it has been fantastic. 

I don't think I'll be looking at TP-Link again in the future for any other products after the poor service in this case. 

This issue also happened to my E4. Haven't tried disabling IPv6 because I don't believe that's the cause. And I also don't want to disable individual mesh, because obvious reason.

update:

I don't know, it seems like it has something to do with the client/device network adapter settings/driver.

Now I'm trying on another laptop (Surface GO), there is no spike..