Circuit breaker trips randomly
You have an intermittent earth fault, probably triggered by expanding metal pinching something

From the symptoms described, this sounds like there is some piece of earthed metal that is heating up and pinching/damaging a wire when it does so, causing an intermittent earth fault.  The heat source can be either environmental or internal, which makes this hard to troubleshoot.

I would recommend a thorough checkout of the circuit's always-hot cabling, with all devices unplugged and all light switches removed, using an insulation resistance tester from both H-G and N-G at the distribution board.  (Your local electrician should have access to one.)  From there, the circuit can be divided into sections by way of the junctions in it for further troubleshooting.