First off what are you calling the ignition module as it won't be the one pictured above?

It sounds to me as it's a loose connection due to it showing itself when you drop the bonnet, check the connector for the CPS and other connections. (This will be located on the gearbox most likely, on older cars it was located by the crank pulley itself)

The ECU fires the spark plugs based on the input it receives from various sensors, primarily the CPS.

It may not be an ECU problem just because they could not read it as there equipment/software may not be compatiable with the ECU.

Martin