Hi, Thanks for the reply. LED lights : Wifi is amber. Power light is off. The sockets reconnect if I power each one off and on again. I have tried moving within 1 meter of the router and assigning static IP addresses. The behaviour is not improved by the changes.

When the issue occurs, the router is rebooted so wifi is not available.  The plugs flash green wifi lights until the wifi is available again after the router reboot.  The plug's wifi light then turns solid amber - at the same time all other wifi clients (various vendors) connect successfully.  The HS100 plugs do not connect until their power is cycled at the wall socket.

@thevilla I am having the exact same problem.  My router is an ASUS RT-AC3200 flashed with DD-WRT v3.0-r40559 std (08/06/19).  I have an IOT VLAN (which is on a virtual wireless network), and if I reboot the router, all other devices on that network reconnect (google home, chromecast etc), except my 5 TPLink smart switches (HS100 and HS110 models).  They try to reconnect, then just stay "orange" like you described.  The only way to fix them is to walk around the house and power cycle them all.

What firmware version did you fall back to to fix the issue?

As a followup to my previous post, I tried downgrading DDWRT to firmware version DD-WRT v3.0-r36527 std (08/09/18) and the issue was resolved.  Thought this might be useful for anyone else with TPLink HS100 switches and DDWRT firmware on their router.

@thevilla try setting a static address for the smart plug on your wifi router. Look under DHCP Server (or similar) in the settings. 

Doing that appears to have fixed my HS110 losing the connection.