Trouble diagnosing an electrical problem

I have a 2010 mk2 Ford Focus estate 1.6tdci style. Recently, I turned the ignition on, and the radio stayed blank. It wouldn't turn on. I then noticed that the interior light wasn't working, nor was the power socket. I don't think the heated rear screen is working either, although the button does light when pressed. All fuses are ok. I have tried unplugging and plugging back in all the multiplugs in the fusebox one at a time. At one point, after plugging the blue plug back in, it all started working again, for a couple of days. However it's happened again and even unplugging the blue plug and plugging back in doesn't work. I have used forscan to check for errors and cleared all the DTCs (obviously and error was logged when I unplugged the multiplug). I have searched the internet and can't find anything about this problem specifically. If anyone can help, I would be extremely grateful.