It’s a learning process and the machine isn’t smart, it relies on you for smarts and common sense.
I keep a bottle of loctite 242 handy and any bolt that comes loose twice gets a single tiny drip of loctite on the threads to stop it vibrating loose. I also twang my belts at least once a week, you can use your phone to check pitch but after a while you get the hang of twanging all three and listening for the pitch changes.
I have also got in the habit of, when I first rapid the machine to the front to insert the first cutter, holding the spindle by the collet (when it’s not rotating…) and giving it a gentle waggle left / right and front / back. If I feel anything knocking or loose then I go through the whole preload check on V wheels, set screws on pulleys etc. to find out what’s loose. After a few tries you get a feel for what the flex should be, just don’t gorrila it, you only need a few Newtons (or pounds) to feel if something is loose.