Blue Tit Nesting box - Attacked

Hi, 

we have had blue tits nesting in our garden for over 20 years and this year we bought a pre-made nesting box. Previously my husband had made our boxes with plastic around the hole but this one doesn’t have it.
The birds have been nesting well up until today, when we noticed something had stripped away the wood to the entrance of the box. 

what would have done this, would this be something like a magpie? 

I can’t hear the chicks anymore so I’m hoping they all flew the nest ok ?