CHT drops sharply

There is too much thermal mass in the cylinder head for the temperature to drop by that amount in 2 seconds so it is likely to be a wiring or sensor fault. I would visually check the connections and wiring and if it all looks OK, I would swap the sensors and see if the fault moves to the other cylinder. If it does, you will need to replace the sensor.

If that doesn't resolve the problem then is there any chance of the ignition system interfering with the signal from the sensor?

Sounds most likely like a lose connection at the CHT probe or a bad connection along that wire. . Check the spade connector on cyl. #2 and make sure it is a firm connection and not lose and wobbly.

Many thanks to everyone for the replies. As you suggested, the problem is solved by cleaning the connectors.