strawberrylini If you are using the MCCC and are using a certain module that I can't mention here, that will do that. Usually, it happens the first few times the sims woohoo. If you are using other mods that you didn't mention that affect woohoo, some of them will also cause that. For further info, you should ask at the MCCC Discord server.
It also happens without mods too but that is usually when the sims involved are woohoo partners. It will also happen when the bars are barely far enough to give you the romance woohoo option, I think. I'm not sure but it seems to happen more often on the lower quality beds that aren't upgraded as well. Like I said, not sure about that last. Another thing that may be a factor is the sims' compatibility and what likes and dislikes they have.
Hope this helps.