Sims refusing woohoo with full romance bar

I have two sims that are engaged and they have a full romance bar but every time l try and get them to woohoo they refuse? They will do all other romantic interactions apart from woohoo. This is a new thing that’s happened in the last two days. The only thing that’s changed is that they now have the ‘fear of being cheated on’ fear. Anyone else have this or know what may be causing the refusal? 

thanks 😊