A server that sits on Starting or Stopping and does not move on is usually a process that has stopped responding, not lost data.
Give it a moment first. Stopping asks the game to shut down cleanly, and a large world can take a while to save. A minute or two on Stopping is normal.
If it does not move, use Kill. The power controls include a Kill option, which ends the process immediately. Use it only after Stop has had its chance: Kill skips the save, so anything not yet written to disk since the last save is lost.
After a Kill, start the server again and watch the console. If it hangs in the same place every time, the console output around the point where it stops is what identifies the cause — include those lines when you contact us.
Do not reinstall or reset the server to fix this. That erases your world and almost never addresses what caused the hang.
If you need help with this, please submit a ticket.