How to use security dfu in app

Question

I used the example in nRF51_SDK_9.0.0_2e23562\examples\dfu\experimental, the first time that work well. But when I want to update a app in app(with dfu function),it failed. (When I use normal dfu ,both work well)
The nRFConnect-4.3.2.apk tool show debug info:
…… 
 [DFU] jump to bootloader send (op code = 1, uploade mode = 4)
[DFU] disconnected by the remote device. 
 …… 
 Why disconnected? How to resolve it

Petter Myhre · Accepted Answer

Could you explain a bit more about what you have done and what you want to achieve? What SoftDevice are you using? You flash the SoftDevice and a bootloader, then you do DFU with which application? Then you do DFU again? With what application?