Hash not found (8) attempting to DFU ipc_radio image (nRF5340, NCS 2.9.2)

Question

I’m working on an nRF5340 project (NCS 2.9.2) with simultaneous multi-image DFU using MCUboot, MCUmgr (SMP over BLE), and external flash (MX25R64, like the DK). 
 App-core DFU works correctly. Net-core DFU ( ipc_radio ) uploads successfully, is reported as bootable and pending, but after reboot it disappears from the image list and Device Manager reports “Hash not found (8)”. 
 I tracked this down to the net-core image not being signed / versioned correctly:

DFU ZIP contains peripheral_uart.signed.bin (app core) but only a raw ipc_radio.bin (net core).

After enabling CONFIG_BOOTLOADER_MCUBOOT=y for ipc_radio , the build fails during signing:

imgtool sign … --header-size 0 … 
Error: Invalid value for -H/ --header-size: Minimum value is 32

I attempted to set CONFIG_ROM_START_OFFSET=0x200 (and searched for MCUBOOT_HEADER_SIZE / related options), but the value is still resolved as 0 in .config , likely due to sysbuild/partition manager overrides. 
 Partition Manager layout appears correct for nRF5340 simultaneous DFU:

app-core secondary in external flash

net-core secondary in external flash

net-core primary via ram/flash simulator

The core question is: What is the correct way in NCS 2.9.x to produce a properly signed/versioned net-core DFU image (with non-zero MCUboot header) so that b0n/MCUboot will accept the hash and it persists after reboot? 
 Is this expected to be handled via:

child-image config,

sysbuild config,

partition padding for cpunet,

or explicit imgtool args for the net-core image?

I can’t easily capture UART boot logs, but I can share partition reports, .config snippets, and the exact imgtool command line if needed.

Aleksander Nowakowski · Accepted Answer

Mind, that with nRF53 the only working mode is "Confirm only". This is because the netcore cannot restore its original image after the new was set to "pending" and swapped. 
 When the TEST command is sent, the netcore permanently changes its image to the new one. When using "Test and Confirm", after reconnection the library (and app) tries to send CONFIRM command using the same hash, but the device no longer has access to the hash as it cannot access the netcore image, thus returning "Hash not found". 
 Change mode to "Confirm only" and you should see the result as success. Note, that in this mode the phone won't reconnect to the device, and the success will eb returned "estimated swap time" after the reset command was sent. Please measure the actual swap time (time until your device starts advertising again) and set the correct value. This is to prevent a timeout on reconnection in case you try to reconnect to your device after getting success (Android has a ~30 sec timeout).

Hash not found (8) attempting to DFU ipc_radio image (nRF5340, NCS 2.9.2)

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