Sweet Chestnut shrivalling leaves and die back
 

I have a few small Sweet Chestnut seedlings (seeds started this year)
that have always had shrivalling leaves (a bit like aphid attack on
blackcurrants) the main stem then dies back almost to ground level.
But it then reshoots from the base, with 2 or more shoots. These grow
only so far and then the leaves shrival and die back.

Its not sun scorch by the way, as I have tried shade..

Any ideas.

As I have a few more that are flourishing well, but from a different
tree.