core/server/src/binary/mapper.rs:60-62 conditionally writes iggy_server_semver only when Some:

if let Some(semver) = stats.iggy_server_semver {
    bytes.put_u32_le(semver);
}

When None, zero bytes are written. But all SDK deserializers (Rust, Java, and the new binary_protocol crate) unconditionally read 4 bytes here, using 0 as the None sentinel. If the server ever sends None, every field after semver gets shifted, corrupting the entire stats response.

The same issue exists in core/binary_protocol/src/responses/system/get_stats.rs:151-153 (semver) and lines 167-171 (where threads_count, free_disk_space, total_disk_space are also conditionally skipped when semver is absent).

This is not critical because it is currently unreachable because the server always derives semver from CARGO_PKG_VERSION via SEMANTIC_VERSION.get_numeric_version().ok(), which succeeds for any valid version. But it's a latent correctness issue.

Fix: bytes.put_u32_le(stats.iggy_server_semver.unwrap_or(0)); and always write the tail fields unconditionally.