I saw an electrician who did know what he was doing change a fuse board incorrectly. He accidentally swapped one end of two different ring mains so that they we

I saw an electrician who did know what he was doing change a fuse board incorrectly. He accidentally swapped one end of two different ring mains so that they were in different breakers! Same result as yours. Always test every live wire. Those glowing voltage sniffer screwdrivers can be pretty handy.