SDK 3.4.0 build/flash issue

I'm having strange behaviour after switching to 3.4.0 on nrf9151. Our existing application was working well on 3.2.0 but showed no life with 3.4.0.

To demonstrate, I built hello world sample with 3.2.0 and flashed and it worked as expected.

I created a new copy of sample hello world, tried to build it with 3.4.0 sdk and toolchain.

The build and flash produced no errors. When the device resets after the flash it still runs the old code.

Running erase and flash means nothing runs.

Having checked the partitioning is the same, I think it's related to TFM -- only the ns build doesn't run.

I'm on ubuntu 24.04. I'm slightly surprised "hello world" doesn't work straight out the box.

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