I'm curious about this because I have generally found the suction to be somewhat painful, and to me pain (even mild) indicates that something is not as it should be. Also, given that extended amounts of suction on other parts of the body can cause changes/problems (think of hickeys - those are due to broken blood vessels), it makes sense to me that strong suction on the cervix could do the same. I'm looking for answers grounded in science rather than random conjecture.
Background: I tried The Keeper years and years ago when I was 18 without much success, but my vagina was also not very used to having things in it at that point. Years later I tried a Divacup, and while insertion was fine, I remember feeling like having it in was painful - not for the space it was taking up, since other penetration is fine, but presumably due to the suction. Instead cups are fine, and are my current prefered menstrual product, but I'd prefer something reusable and would generally like to explore other options again.