Hello
Flossing regularly is a good practice, and when u have had crowns it will help u maintain yout crowns as well as your teeth for long term... So basically flossing helps cleaning between your teeth.. if hygiene not maintained gums will get inflamed leading to bleeding..hence it's normal for gums to bleed if not hygienically maintained
Next Steps
floss regularly apart from brushing twice daily
Health Tips
Every six month visit to your dentist will give u a better oral hygiene