High Current 400ms+ Startup Delay BLE Beacon Using RC Oscillator

Question

Setup: 
 - VS Code - NRF Connect v 2.1.0 
 - Hardware: NRF52840-DK @ 1.8V 
 - Application: BLE Beacon ( https://github.com/zephyrproject-rtos/zephyr/tree/main/samples/bluetooth/beacon ) 
 KConfig/prj.conf:

CONFIG_BT=y
CONFIG_BT_DEBUG_LOG=n
CONFIG_BT_DEVICE_NAME="MyName"
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=n
CONFIG_BOARD_ENABLE_DCDC=y

I have disabled the LFXTAL and enabled the RC Oscillator as the clock source to reduce startup time, however from cold boot I am seeing a ~430ms period of inactivity that is running @ 4mA.

If I change my clock settings back to use the XTAL then another 400ms (expected) period is added for a total of 800ms of no BLE activity:

Yes I have powered cycled after programming. Yes I have performed a Pristine build. 
 
 When I load up the same BLE Beacon firmware from NRF5 SDK with the same clock settings, I DO NOT see this 400+ms delay. This looks to be specific to NCS/Zephyr. 
 Screenshot of NRF5 SDK sample code with RC oscillator as soft device clock:

I saw this post: nRF52840 startup delay 
 However this setting: CONFIG_ENTROPY_CC3XX=n causes a build error.

Any idea why the default NCS/Zephyr implementation for the BLE Beacon has this 400+ms delay before any BLE beacons are sent and why its at ~4mA? 
 Is there some additional KConfig setting I need to change?

Susheel Nuguru · Accepted Answer

Please add this in your proj.conf to disable CC3XX backend and use nrf rng backend instead 
 CONFIG_HW_CC3XX=n
CONFIG_ENTROPY_CC3XX=n
CONFIG_ENTROPY_NRF5_RNG=y
CONFIG_CC3XX_BACKEND=n 
 and add this to your ovelay file 
 chosen {
 zephyr,entropy = &rng;
 };

High Current 400ms+ Startup Delay BLE Beacon Using RC Oscillator

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