Update:
Just contacted BA via their Customer service chat , couldn't really find anything definitive as to what happened so they suggested we open a ETAM ticket ? which we did. Essentially their customer services said they was not able to see what their colleague at Heathrow did to clear the boarding pass problem. They said if it was something significant then normally a new boarding pass would have been issued .This was not the case just a question of re-scanning the original App Boarding pass which was accepted after the action by the BA desk. They did agree that a Visa was not needed for this journey. So lets see what feedback we get to the ETAM. Just hoping one way or another we can avoid a repetition of this.