There can be a lot of resons.
- Wrong soil
- too much water
- too low temperature of the soil
- deseases
The 3 most important things for A. titanum are : the soil, the watering and the temperature.
Soil : it must be a well drained soil
temperature : Never let the soil cool out lower than 20 °C
Watering : The soil should be moist, but not wet.
Here we have a culture sheet of A.titanum for download. It´s made by botanical garden of Bonn :
Culture Sheet
Regards
Stephan