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.

@BigCanoe 

Hi, sorry for the delay.

We would like to follow up on your case by email later.

And could you please help me check the following information:

1. When the KP105 showed up as local only, could you still control it via Google home app and via voice from a Google home device?

2. May I know the model number of your home router?

3. Both of them have the same issue, right?

4. Did this issue start since you bought the plugs?

Thank you very much for your understanding and support.

@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

@BigCanoe 

Hi, thank you very much for your kind reply.

We would like to follow up on your case by email and forward to our senior engineers for further help.

Please have a check of your email box later.

Thank you very much.

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.