Why doesn't the scan_evt_handler get called in the ble_app_uart_c sample under nRF5_SDK_17.0.2_d674dde conditions?

[Takashi_hei]

Why doesn't the scan_evt_handler get called in the ble_app_uart_c sample under nRF5_SDK_17.0.2_d674dde conditions?
I've tried various things, but neither scan_evt_handler nor ble_evt_handler gets called.

[Takashi_hei]

Thanks for the advice.

<info> app_timer: RTC: initialized.
<info> app: err_code = nrf_sdh_enable_request:0
<info> app: err_code = nrf_sdh_ble_default_cfg_set:0
<info> app: err_code = nrf_sdh_ble_enable:0
<info> app: err_code = nrf_ble_scan_init:0
<info> app: BLE UART central example started.
<info> ble_scan: sd_ble_gap_scan_start:Scanning
<info> app: Central;Scanning started

What is NRF_SDH_BLE_OBSERVER run3?

NRF_SDH_BLE_OBSERVER(m_scan_observer, APP_BLE_OBSERVER_PRIO, nrf_ble_scan_on_ble_evt, &m_scan);

NRF_SDH_BLE_OBSERVER(m_ble_observer, APP_BLE_OBSERVER_PRIO, ble_evt_handler, NULL);

Is the above correct?
Is anything else needed?