Unusual to have to replace a switch on such a new installation?
However, what you appear to have is a Triple & Earth between the two switches and a TW&E switch drop - correctly sleeved. You should be able to see which groups of wires come from which cable - the TW&E will be brown and blue sleeved brown, the triple brown grey and black. That the browns are a different shade is a red herring...
Below is the wiring diagram for a two way switch - ignore the centre intermediate.
L1 L1 0===========0 0===========0============= Line | \ / | C 0================================O C \ / \ / 0===========0 0===========0============= Switch return L2 Optional L2 Intermediate You really need to check the switch at the other end of the two-way circuit as there isn't a standard set in blood for which colour goes to which terminal as regards the triple cable. However, if you can't just experiment until it works - you won't blow a fuse or whatever. Just keep the switch pair wired to L1&2 - that doesn't vary.
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