Apple - Problem in new growth

Nathan in Syd starts with ...
I have a couple of dwarf apple trees that have been growing well but recently many of the new sprouts seem to be getting attacked by something and shriveling. Those sprouts seem to have been hollowed out inside. There are other sprouts on the same tree that are vibrant and healthy (though the proportion is increasingly moving in a negative direction). I'm not sure if it is the same thing but a spicezee tree is also getting shriveled growing tips.
Does anyone have any idea what might cause this and how it could be treated?

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