BBC iPlayer and the instances have been to numerous to remember. The point is that whenever this happens I access Chromecast immediately and can resume the programme from the same point and it will continue to play without issue.
TBH I should learn and simply use Chromecast as the player of choice.
Due to this issue I ended up buying a second Chromecast for the other TV. We dont have any issues with any of the other players e.g. ITV hub, Netflix or Youtube etc.