Da14683 Not coming out of sleep on internal RC timer

Does anyone know why the DA14683 would not come out of sleep mode?

We have a setup that from a hardware point of view is identical to the development daughter board DA14684 DB AQFN vD.  If we run the code on the daughter board powered on its own by a coin cell it goes to sleep and comes out on the 5seconds on 5 seconds off cycle we have set.

Running the same code on our board it works for a few cycles then stops. Totally baffled, help please.