Some duplicants refused to go on massage beds even when priority was on 9 and no other jobs were assigned to them. In that case where they had no Jobs assigned, they just idled. It took me some sessions to find that bug, so it may not be easy to reproduce it, hope there's a way of fixing it! Thank you for the attention.
Create a world and start to build your home. After having a big place, have some duplicants stressed and start creating massage beds. Assign some of your duplicants to use them. If they refuse to use it oh the first place, start increasing priority. If even on priority 9 they still refuse it, try unassigning them of any Jobs they had.