If the WebM container has chapter or stream metadata, we copy artist / title / album fields into the FLAC container where the FLAC format supports tags. Otherwise the FLAC file is untagged — use a tag editor (Mp3tag, Picard) post-export for richer tags.
Silent gaps usually mean the WebM file had a multi-track audio layout and we picked the wrong stream. Use the "audio stream" option to explicitly pick stream 0, 1, etc., or re-mux all streams to a multi-track FLAC container where FLAC supports it.