If the WebM container has chapter or stream metadata, we copy artist / title / album fields into the MP3 container where the MP3 format supports tags. Otherwise the MP3 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 MP3 container where MP3 supports it.