I forced an assert in radio_event_adv_prepare by setting
"_radio.tocker_id_prepare = 1”. All I see is:

***** HARD FAULT *****
Executing thread ID (thread): 0x200007a8
Faulting instruction address: 0xbc76

No additional logging.

[vich]
Are you using the upstream master as-is? Or you have modified the default configurations?
BT_ERR message when ASSERTing should be printed out on UART by default for the peripheral sample.