your CU is a mess! what clowns have been playing with it? mixing Mcb's like that is not a good idea
CU's are designed for specific Rcd's / Mcb's
I would recommend getting a Qualified Sparks to test the circuits properly, that means test the wires, the Mcb, the Rcd and every connection to every socket. if necessary split to 2x radial circuit, connect 1 only and test moving the split socket by socket
then you should find the cause of the problem or the location between 2 sockets at which point you can replace the cable between the 2 and see if the tripping ceases.
CU's are designed for specific Rcd's / Mcb's
I would recommend getting a Qualified Sparks to test the circuits properly, that means test the wires, the Mcb, the Rcd and every connection to every socket. if necessary split to 2x radial circuit, connect 1 only and test moving the split socket by socket
then you should find the cause of the problem or the location between 2 sockets at which point you can replace the cable between the 2 and see if the tripping ceases.