Hi,
Still have no answer for this problem, so I repeat again.
I have got the reply that the bootloader do not impact the application, so please check these videos.
VIDEO 1:
1.erase chip
2.program soft device
3.RTT Viewer logging
4.application working normally
VIDEO 2&3:
1.erase chip
2.program soft device
3.program bootloader
4.DFU with nRF connect
5.RTT Viewer logging
6.application working error