https://github.com/sigp/lighthouse/blob/cc2e2103645be3fa31c3d2397147192ccf6f1a25/ssz/src/impl_encode.rs#L50 Presently, SSZ prefixes a Hash32 with a length prefix. It should not do this, as a Hash32 is fixed-length and does not need a length prefix. When this is implemented, it will break the `SszBlock` struct. I am more than happy to fix that struct personally when the time comes.