Indeed - not only do you need to remove that timer thing, you also need to plug the PLC directly into a wall socket. The length of cable on the power strip adds a big amount of signal loss and noise.

Seems like you look at a disturbance on the power lines. Investigate whether some large electrical equipment nearby turns on or off at that exact time. Might be street lamps, a smart heating system,...

You can also reset them by pressing the button for VERY long, until the LEDs show you they're restarting. Then you can proceed to pair them with regular one-second button press.

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If you set a device to a fixed IP address, you better choose one that is outside your router's DHCP numbers range. Better yet, if your router supports that, leave the device on DHCP client mode, and...

You need to press that Pair button for pretty exactly one second. If successful, the "powerline" LED on the adapter should start blinking. Alternatively, you can pair the new one into the existing...