libcamera doesn't build reproducibly

[KP64]

When trying to host any service that needs libcamera (e.g. stirling-pdf) on my Raspberry Pi 400, it compiles from source and fails at different point in times of compilation in each attempt.
Is it intended that libcamera even compiles from source, i.e. is it not provided in the cache?

The cache is correctly setup and I haven't modified any of the inputs of the flake.
Here is my config if it helps.