Has the bed been 'made up' or not? You know, is the blanket pulled back, or is it tidied up?
If the bed is still in a 'messy' state, there's a possibility that the sim is prevented from using the bed because the butler is being pushed to "make bed", but for some reasons can't do it. This will block your sim's routing.
This explains why replacing the bed 'resets' the blocking, because new beds arrive always in a 'tidied' state.
I'm not sure how to fix this, because I never experienced it. But here's a suggestion: Pause the game, reset the butler's queue (IIRC possible using Nraas Master Controller), tell your sim to make up the bed, queue the next action (relax/sleep), then unpause.