I have also made 3 unlucky attempts at growing D. Adelae. Every time I try to grow an Adelae, it seems to end in failure.
Luckly I saved some cuttings before all my mother plants died.
I have tried different soil types such as LFS alone, 50/50 peat,perlite 50/50 peat, LFS 50/50 peat,vermicultie and it made no difference. I'm pretty sure its not a light issue so it's got to be humidity.