@Adam-  Hi ive just had this problem today with my adapters flashing red and green. I have been decorating for a few days and had removed them all from the wall sockets and when I put them all back into the wall sockets they began flashing red\green.

So I done as everybody else has done turn them on off , move them to different locations and try to link them back together. However by chance I reset each of them by holding the button on the side down for 15 seconds or so until the unit flashed orange on 1 of the lights to say it was done resting them and did the process of linking them all back up 1 by one and this worked for me.

Dont know if this helps anybody but it has to me

@Kev_N 

I just bought the Ubiquiti Amplifi Mesh Router instead. I couldn't be arsed having to reset my TP-Ling every month or so as I've had to do. The Ubiquiti is working great so far. I now have two AV2000 kits if anyone wants them...

@Adam- Just to say, I had (but fixed) the same issue of a system that had been running for a month or two but suddenly became very unstable to the point of utter uselessness. Loads of packet loss and slow pings and dreadful throughput.

Re-pairing the devices didn't work. Long hold of pair button didn't work either.

What worked was manually adding the Powerline Key of the remote devices to the main device. This populated each device and showed the tx and rx speeds of each. I needed to do this whilst they were close together or it failed. 

See section 3.2.1 of the manual for instructions.

@FixedTheNoPow 

The is for the reply but I put these in the bin. I have the Ubiquity Amplify gamers edition now and it has been perfect.