LO is not shutting down completely

If I’ve used LO for a while, when I shut it down, it’s still in memory. I close documents correctly (Alt F C) and close the program with the File menu. But when I run Task Manager it shows five or six instances of LO still in memory (and occupying a lot of memory). I noticed this when my programs slowed down and the cursor got way behind the mouse movement. When I shut the instances of LO using Task Manager, the mouse and programs worked normally. How can I get LO to shut down completely?
Thanks for your answer.