I am having this issue too where my Sims will not go to the side of the bed assigned. He/she will keep going for the opposite sidewhere their partner sleeps waking him/her up. No matter how many times I click the one side of the bed they dont want to comply. Nothing is blocking it so that isn't the issue. I did the switching the beds thing myself and that didn't work at all for me.
Even sitting on the bed interactions have gone screwy. If I want a Sim to sit on one side of the bed he/she always goes to the other side and if I want two Sims to sit on the same side to chat, kiss, or snuggle one Sim ALWAYS goes to the other side of the bed every time no matter how many times I click the side I want them to go to on the bed.