Amazon alexa app doesn't include Transition Time field in SIG mesh message

Question

I write a mesh light controler demo for my device,it include Configuration Server model,Health Server model,Generic OnOff Server and Light Lightness Server,the device can be controled by Amazon alexa app through a Amazon Echo Dot normally. But I hope to the lightness of the light can be changed with transition,sig mesh message may optionally include a Transition Time field to indicate device to use transition,but messages from alexa always have no this filed to my device,I don't know the reason but I have found Transition Time field include in same message when it send to other brand device. maybe some feature not support in my device?I don't know,please give me some advise,thank you