Off the lighting circuit upstairs, we have the shaver socket in the bathroom (originally part of a different circuit when we moved in and not protected by the RCD, we swapped that over but that was a long time before the issues), the combi boiler and bathroom extractor run off that circuit as does a power socket in the loft which is not used for anything.
No alarms, doorbells,no fridges. It’s tripped when we’ve been out of the house so the only thing that might draw a current while we’re out is the boiler. But we’ve had spates in the warm summer months and colder winter times.
I’d even suspected a short in a celing rose that might move due to variation in temperature.
I also thought of splitting the ring into two lines to narrow down which light fitting/join it might be, but I can’t replicate the fault so could be waiting several months between trips.