In current FFmpeg, whenever Matroska with ProRes is demuxed it creates an atom that is just 8 bytes short of the true size necessary.
We can work around this by padding the actual packet by 8 0x00 bytes, which should result in older FFmpeg versions working fine.
An FFmpeg patch is available: http://ffmpeg.org/pipermail/ffmpeg-devel/2019-September/250724.html