Just to add to this, it appears that the devices occasionally show up while on 4G... But only intermittently. 

If anyone from tplink support checks these forums, I have a pcap trace of the traffic from boot to"local only* including turning off and on in the kasa app and via Google home. Hopefully that should provide sufficient material to work out what is going on.

@TP-Link 

thanks for the response

1) yes, when it shows up as local only I am able to turn it off and on using the google home app or voice via our google home mini if i am on the same wifi network (I can see in the traffic that the KP105's are communicating with the home mini on port 9999). When i am on 4G however, the google home app shows the KP105's as offline most of the time and i cannot properly control them but the do occasionally seem to work.

I have a packet capture from when the google home app definitely indicates the devices as offline but i managed to make one of them work. The device is talking to an AWS host at 34.197.7.30. (use1-api.tplinkra.com)

2) the router is a Mikrotik RB750GR2 and the access point is a Mikrotik RB951G-2HnD (this is prosumer grade equipment and the main router is set as the AP controller... i have very good visibility and control over what is going on on the network including ability to capture packets to/from the KP105's). Firmware in all cases is the latest 6.47.8.. I have three access points in the house and in each case the KP105's are in the same room as the AP's the distance to the AP is about 4m. 

3) yes, both have the same issue. I have no other issues on the network and the speed, ping times etc are  stable. There are multiple other devices working well on the network. Broadband speed is 50/10 megabit

4) yes, this issue has been there since i bought the plugs (i bought them last week)

@TP-link

Anything?? 

I'd really like these to work properly

 (or know that they won't do I can return them)

Thanks

I'm just leaving a note in case others find this thread and have similar issues

It appears that the KP105 running firmware 1.0.5 has a bug in handling DNS and possibly DHCP

If your router is not on x.x.x.1 the KP105 will incorrectly send DNS packets to x.x.x.1 anyway which do not get a reply so the KP105 does not know how to reach its cloud servers  and goes to local only mode (despite having previously received a correct DNS response with the right addresses)

This was only found through packet tracing and there being a device (not a router)  on x.x.x.1 on my network. In my case the Mikrotik has build in packet trace and capture which made it possible to find. Special thanks to some gurus on mikrotiks forums for finding the issue.

It's been reported to tp-link support.

Moving the router to x.x.x.1 appears to have made it work properly but the bug needs fixing.

To fix this on my end, I opened the device within the Kasa app, clicked on the Cog (top right) and there was a button at the top (it disappears once you tap it, so I can't remember what it says).

This stops the device being local only, and will now appear in Google Home.

  @BigCanoe all the kasa devices will blat your lan with malformed dns queries. it's been like this for years - they don't care. they've polled our lan, hashed whatever they can glean about where you shop for mac addresses and left you with a mess of devices in the wrong multicast groups. you will at some point trip and firewall yourself hehehe

  @Ricky666 

thanks... I sort of guessed as much but have not bothered to chase down packet traces etc.

its working fine since I moved the router to x.x.x.1 

I'll hve to look at my pi-hole and see if dns queries are going there or not

my own solution is going to be to vlan off all IoT devices in the near term anyway (and only give the well behaved ones internet access perhaps)

Mikrotik does a pretty good job of such things afaik... just another SSID for IoT (going to add a camera which is the impetus for tighet security

there have been two firmware updates since i posted this but I have no idea if anything has been fixed.