external flash wake up DA14585

Hi Dialog,
I am using the sample code: ble_app_peripheral from SDK 6.4.2.
Ionlymodified the variableapp_default_sleep_modefromARCH_SLEEP_OFFtoARCH_EXT_SLEEP_ON
I am very confused...If I burn the code into RAM (SmartSnippets -> Booter -> Download), it works.
However, If I burn it into external flash, it will advertise but just a while. The mobile app can find the device but the device disappears almost immediately.
It seems like DA14585 doesn't wake up sfter sleeping...