I'm no expert but you could try disconnecting and then reconnecting to your internet. It's worked for me in the past.

EyeOfTwilight wrote

I'm no expert but you could try disconnecting and then reconnecting to your internet. It's worked for me in the past.

Thanks for the reply. I've rebooted the modem/router a few times but it makes no difference.

Additional details added to original post.

How about status of Signal light on your WA860RE?
Did you connect PC to main router and PC to range extender by wire or wirelessly to do ping test?

The unit shows two green lights on the front - the top and bottom ones.

The tests were done over a wireless connection. The computer isn't near enough to the router to use a wired connection (I don't have a long enough wire!). I may be able to do this tomorrow with a different workstation if it's important though.

That the top signal light is solid green indicates the good location of WA860RE.
Try cable connection to range extender. It should be better than wrieless connection to WA860RE.

Did you get a resolution to this? I brought this unit and getting the same issue. Even a device connected via ethernet to it is pinging other wireless devices with high latency. Worse still a ping to the extender over ethernet is produce poor results...

Reply from 192.168.0.111: bytes=32 time=269ms TTL=64
Reply from 192.168.0.111: bytes=32 time=79ms TTL=64
Reply from 192.168.0.111: bytes=32 time=62ms TTL=64
Reply from 192.168.0.111: bytes=32 time=77ms TTL=64
Reply from 192.168.0.111: bytes=32 time=41ms TTL=64
Reply from 192.168.0.111: bytes=32 time=15ms TTL=64
Reply from 192.168.0.111: bytes=32 time=71ms TTL=64
Reply from 192.168.0.111: bytes=32 time=103ms TTL=64
Reply from 192.168.0.111: bytes=32 time=13ms TTL=64
Reply from 192.168.0.111: bytes=32 time=1ms TTL=64
Reply from 192.168.0.111: bytes=32 time=2ms TTL=64
Reply from 192.168.0.111: bytes=32 time=48ms TTL=64
Reply from 192.168.0.111: bytes=32 time=164ms TTL=64
Reply from 192.168.0.111: bytes=32 time=273ms TTL=64
Reply from 192.168.0.111: bytes=32 time=253ms TTL=64
Reply from 192.168.0.111: bytes=32 time=52ms TTL=64
Reply from 192.168.0.111: bytes=32 time=65ms TTL=64
Reply from 192.168.0.111: bytes=32 time=1ms TTL=64
Reply from 192.168.0.111: bytes=32 time=1ms TTL=64
Reply from 192.168.0.111: bytes=32 time=27ms TTL=64
Reply from 192.168.0.111: bytes=32 time=108ms TTL=64
Reply from 192.168.0.111: bytes=32 time=5ms TTL=64
Reply from 192.168.0.111: bytes=32 time=166ms TTL=64
Reply from 192.168.0.111: bytes=32 time=41ms TTL=64
Reply from 192.168.0.111: bytes=32 time=48ms TTL=64
Reply from 192.168.0.111: bytes=32 time=34ms TTL=64
Reply from 192.168.0.111: bytes=32 time=13ms TTL=64
Reply from 192.168.0.111: bytes=32 time=1ms TTL=64
Reply from 192.168.0.111: bytes=32 time<1ms TTL=64
Reply from 192.168.0.111: bytes=32 time<1ms TTL=64
Reply from 192.168.0.111: bytes=32 time<1ms TTL=64
Reply from 192.168.0.111: bytes=32 time=94ms TTL=64
Reply from 192.168.0.111: bytes=32 time=1ms TTL=64
Reply from 192.168.0.111: bytes=32 time=55ms TTL=64
Reply from 192.168.0.111: bytes=32 time=1ms TTL=64
Reply from 192.168.0.111: bytes=32 time=42ms TTL=64
Reply from 192.168.0.111: bytes=32 time=69ms TTL=64
Reply from 192.168.0.111: bytes=32 time=17ms TTL=64
Reply from 192.168.0.111: bytes=32 time=40ms TTL=64

Well, it seems that sometimes the delay is high. Maybe you can change the wireless channel.

Changing a channel would have no affect considering those ping replies are over the ethernet port of the extender.
I flashed OpenWRT onto the extender and it resolved the issue. Sadly I cannot get it to bridge the wifi to the ethernet so this is still not an answer. It does prove though its a TP-Link firmware issue.

I just bought this same device 2 years later and it still has the same issue, is there a solutiuon yet?

 

In my case it's even worse, there's massive packet loss.

 

Also tried the latest firmware: TL-WA860RE(EU)_V5_181108 and the issue persists, might have to return the device.