Interesting device by the sound of it.
I had similar trouble about one year ago. So I did a routine PAT test with the 'yellow hand-held' on all items connected to that ring. (I do that throughout the house every 12 months as a matter of routine.) The kettle in the kitchen looked highly suspect.
Then I remembered the symptoms. Often - but not always - the RCD would trip during the night - sometimes when I was asleep; sometimes when I was awake. (I am a dedicated 'owl'
). Whenever I go to bed, I make myself a nightcap - usually 'Horlicks' substitute. But during the day, the kettle gets a lot more regular use: it's empty, refill (enough for two cups plus a bit), boil; make drinks; kettle then empty, or very little water remaining in it. Repeat sequence as required. But overnight there was plenty of undisturbed time for water leakage through to the mains connector and only one drink had been made: much more water left in the kettle. (It was an old 'Swan' kettle.) Replacement of that aged kettle solved the problem.
Al.