Hi All
i have had one of these doing exactly the same took me ages to figure it out thinking along the lines already mentioned instruments and immo kept going round in circles we had faults in engine and immo and instruments we were lucky enough to geta donor car and swapparts it turned out to be engine ecu.
I gave RMIF helpline all the details as i was in talks with them regarding the immo circuit and instruments.

When fault was present i lost comms with engine ecu.