moulting problem in Extatosoma tiaratum

Anyone help?

When the insects get to about midsize they get stuck in the moult - halfway out and i find them laying on cage floor quite flaccid and dead.  Is it humidity, temperature or feed?  I feed on bramble, they are misted once a day and kept in a mesh cage and in a warm room (not excessive heat).

any thoughts?

Stephen (UK)