BitArray not deserializing

[slrx4]

When I deserialize BitArray in Unity it just returns an empty BitArray (not null) with 0 length. Everything else is working great. This is how I deserialize:

using (FileStream _fileStream = new FileStream(_path, FileMode.Open, FileAccess.Read, FileShare.Read, 4096, true))
{
    chunkLocal.Chunk = await MemoryPackSerializer.DeserializeAsync<Chunk>(_fileStream);
}

but I tried other deserializing approaches too, still other fields are working but not the BitArray. It seems to be serializing correctly because I can see the file size growing. Am I missing something? Do I have to do some extra stuff for BitArrays?