Had something similar a while ago where we were putting in a couple of RCBO boards to replace the 3036 boards, it quickly became apparent the multi gang switches and neutrals were not properly paired up, the installation had a 6 gang and 13 gang switch (18 gang grid 13 used), the 6 gang had 2 banks of 3 switches on 2 lives and 2 neutrals this ended up as a bank of 2 and 4 to get the lives and neutrals paired, the 13 gang
had groups of 2, 3 or 4 switches on one live and 2 or 3 neutrals it took a little while to unravel and get the switches grouped across the 4 lives and 4 neutrals but got there in the end.
What was interesting was the 5 yearly EICR's for the last 20 years had not found it but that's another story