is there supposed to be sex animations while your breeding monsters?
Not for all combinations, but mostly all "Male+Female". You have an option for not see the animations "show animations" "green button".
Some animations hidden and unlocked only if you reach a certain level of affection.
If it desapear and before you have them, don't know but i see no blatant bug in the game. Just have some difficulty for find all clues to unlock/ chain quests, story.