the funny thing is that the default uncensor does not show a vagina at all to me

, also knowing that some skins interfere with this feature seems strange to me, as skins does not add bones/blend shapes to the body mesh but body types and uncensors does. i didn't test the dynamic vagina in game but here is a scene with a character using the "bp.sac_roastie" uncensor which has the dynamic bones (no other uncensor supports the feature), i attached a dynamic bone collider item to the lower abdomen part of the body to demonstrate the interaction (doesn't have to be attached at all) ,it should work the same in the H-scene in main game if the male chara has a similar collider on it's parts or uncensor.
View attachment 950033
if you open the attached scene below in studio, select the dynamic bone collider and move it close to the vagina to see the effect it does. try it with other characters and different skins to confirm that the skins you mentioned are preventing it or not.
View attachment 950037