Could have been lack of humidity, poor air flow, low temps or more then likely SADS. Avics are known to just up and die seemingly for no reason at all. They are sadly not very hardy tarantulas. Sorry for your loss
Edit: Could have been from dehydration to. Small slings are known to dehydrate quite eaisly especially avics. More then likely you will sadly never no the true cause though. Sorry agin for your loss![]()