Menstrual cup users..

So I've had a cup for a few months now and every once in a while 1 day out of my period(usually 4 day long) the cup just does not work with me. Does anyone else have something like this happen? I know your cervix moves when you're on your period and stuff but I'm just curious. It's happened twice to me now that I had to take my cup out and switch to a pad for the day and then go back to the cup the next day. Some days the cup works 100% for me and other days I need a liner. 🤷‍♀️🤷‍♀️🤷‍♀️