Replaced LEDs, now no lights in entire house

I'm at my wit's end...I replaced 2 DIY plug-base LEDs and now the rear half the house has no lights at all. 4 LEDs in the same room on a separate switch are the only lights that work now on the light circuit.

The LEDs I replaced remain ON even when their switch is OFF, and they change brightness when using another switch on the same panel. And the light that THAT switch should operate doesn't turn on, but is glowing slightly even when the switch is off.

Everything was working fine until the tenant said the LED was flickering...a simple changeover has turned into a monster job and a tenant living in the dark (I gave her some desklights to plug into the wall for the time being).

Did I inadvertently kick a cable loose when crawling around plugging the new LEDs in? Or is there something more sinister going on? From what I have read, it could be a loose neutral or the switch playing up. I'm calling sparkies up but the long weekend means it is difficult...