Hi there,
So sweet , your using the jlink on the dev board then “DK”
because that read looks pretty correct.? You good with it’s not the on-board nrf52840 but the SWD connected one ? YES!
You can download the Hex from the Xiao Github or Wiki. with the Bootloader. I have attached it here, also hit the Drag and Drop testing Files thread and put it in Bootloader mode and Drag a UF2 file to it.
to test RGB , SD , displays, etc…
Seeed_XIAO_nRF52840_Sense_bootloader-0.6.1_s140_7.3.0.zip (212.5 KB)
HTH
GL 
PJ 
brb got to rescue some cats. 