Investigating RCD nuisance tripping when ACCL changes power source
Short answer: I discovered that the neutral connection for one of the rooms had some fluctuating connectivity with earth. I have since disconnected the neutral from the neutral busbar and turned off the MCB for that room. This mitigated the RCCB tripping problem.
Long answer: https://nikhilapatil.medium.com/rcd-nuisance-tripping-5ca7432370e5