Hi,
I've tried your app (built with trunk FPC) under Sequoia, and it seems to work fine.
One thing I'd suggest though is to enable the threading mode (by adding Application.Threaded := True; before Application.Run;), which would 1) allow serving multiple clients simulatenously; 2) prevent a faulty client from blocking the whole sever (e.g. a client which opens a connection but never sends proper request contents - makes the server wait on its only thread, refusing to accept any other connections) - which indeed may look like the server stopped working completely.