Hi Kevin, 

Current network diagram: I have an ethernet handoff fom my provider plugged into one deco, one other deco using ethernet backhaul and the other wireless backhaul. 

The latency spike affects performance, mostly visible with IPTV and online gaming. 

Here is an example of the latency issue while pinging the public IP address assigned by my provider, so this is still within the home network and is not anyhow related to internet. As you can see I have removed few lines as per the sequence number. Screenshot of the full ping attached. 

64 bytes from 192.168.100.137: icmp_seq=0 ttl=64 time=65.341 ms

64 bytes from 192.168.100.137: icmp_seq=8 ttl=64 time=216.484 ms

64 bytes from 192.168.100.137: icmp_seq=14 ttl=64 time=13.446 ms

64 bytes from 192.168.100.137: icmp_seq=15 ttl=64 time=48.472 ms

64 bytes from 192.168.100.137: icmp_seq=25 ttl=64 time=11.189 ms

64 bytes from 192.168.100.137: icmp_seq=26 ttl=64 time=5.027 ms

64 bytes from 192.168.100.137: icmp_seq=27 ttl=64 time=23.683 ms

64 bytes from 192.168.100.137: icmp_seq=28 ttl=64 time=10.280 ms

64 bytes from 192.168.100.137: icmp_seq=38 ttl=64 time=601.847 ms

64 bytes from 192.168.100.137: icmp_seq=39 ttl=64 time=123.761 ms

64 bytes from 192.168.100.137: icmp_seq=40 ttl=64 time=7.116 ms

64 bytes from 192.168.100.137: icmp_seq=41 ttl=64 time=11.835 ms

64 bytes from 192.168.100.137: icmp_seq=42 ttl=64 time=22.416 ms

I do not have a modem at all, I get ethernet from my provider. I do not have an ethernet port anymore on any of my computers but I'll try to get one and connect to the primary deco directly to see there is any improvement. 

Please also take into consideration the feedback from all other users, the biggest thread is here 

https://community.tp-link.com/en/home/forum/topic/171562

I unplugged all decos and connected an old Asus router and I do not have this issue. 

My conclusion: Something is very wrong with all decos most probably and TP-Link is not doing anything about it, completely useless.