Fault current indicator - what should I do?
Yellow indicator here indicates there was a difference between live and neutral current and the difference is suspected going somewhere it shouldn't.
The fault may be not only in some appliance, but also somewhere between the panel and the receptacles, over the wires hidden in the walls.
Usual reasons include, but are not limited, to:

Moist or water leaking near the wires, receptacles or distribution boxes. The leak may be hidden in the wall for a while.
Insects, dust or mice at the same places (cockroaches?)
An insulation of some wire degraded because of overheating (lighting fixtures?)
Some hard-wired device (that cannot be unplugged) failing. (Water heater is the first suspect, cooker is the second, air condition third)
The protection device itself malfunctioning.

Good luck!