The last company I flew for it was written in the Ops Manual that you were not permitted to accept a line up clearance unless you had secure from the cabin and were ready.
I know that holding point well as we often flew out of Dublin. On one occasion as we lined up we had a call from the cabin that there was a problem having previously been given secure. A quick call to ATC who asked to vacate which we did with no issue for landing traffic. As soon as we vacated called by cabin to say issue resolved advised ATC who promptly slotted us into beginning of queue and we got away. This is what could have happened on this occasion.
Whilst we need to hear the crews side of the story it seems to be poor management of the situation.