MFXInit() returns MFX_ERR_UNSUPPORTED on Apollo Lake

Hi,
We have an application running on Apollo lake that uses MSDK. We have the application working on a different platform, but the version we've built for Apollo Lake MR3.1 on yocto fails when calling MFXInit().

mfxVersion ver = {{0,1}};
mfxIMPL impl = MFX_IMPL_AUTO_ANY;
pMFXSession = new MFXVideoSession();
// We call: (Which in turn calls MFXInit(impl, &ver, &m_session))
pMFXSession->Init(impl, &ver);
// And it returns 3, MFX_ERR_UNSUPPORTED

Looking at the documentation, MFX_ERR_UNSUPPORTED should only be returned if either `impl` or `ver` are invalid.
`ver` should be valid for any 1.x version of MSDK
We have the MR3.1 release of MSDK for Apollo Lake with recipe "msdk_16.7.bb". I assume this recipe version is either unrelated to the msdk version, or it means we have version 1.16.7?
`impl` should be valid if we have any available implementation. We have libmfxsw64.so and libmfxhw64.so both in /usr/lib/ and in the same directory as the app.

It seems pretty opaque to me, what could be causing the error. We are passing the same, sensible seeming (at least to me) arguments as the version we have working on a different platform, but on Apollo Lake we get an error. I suspect it's trying to find some library and failing, but which library?