My experience is that this is quite common. Especially at startups but also at fortune 500s there exist staff engineers who have no team and just exist working on whatever catches their fancy that day/month. The grandparent talked about a month long project which is where these engineers tend to live in my experience. Its not that they get no help more that they jump around and maybe grab someone from the team when theyre almost done to integrate the new feature with the existing codebase.