@irrilia Hey, I also had this problem but im on console. Here’s how i got it to work tho:
1) first i tried it normally but my sim had really high energy so she kept waking up in 2 hours or so but i kept the 6 hours in mind and eventually with enough sleep interactions that i added up to 6 hours nothing happened
2) being very frustrated, I decided to delete the game and its DLC (i have all of them) and then redownload them to get rid of any cache or errors
3) I loaded the save and retired sleeping in the treehouse again but nothing happened
4) I quit without saving and reloaded the game again and this time drained my sims energy bar to exhaustion by going a day without sleeping since she has the seldom sleepy trait and when they were in the red I sent her to sleep in the treehouse
5) everyone in the household i either sent them to sleep or to volunteer so I can quickly zoom past the 6 hours but I can definitely tell you it was more than 6 hours
6) i got the aspiration completed but it was 9 or 10 hours of sleeping in the treehouse without any interruptions
7) I would suggest to wait until your sims energy is really low and then send them to sleep so they can sleep for more than 6 hours in one single interaction
8) if that didnt help either I also had a even worse experience with the mind and body aspiration but I got it to work by changing the aspiration to a completely different one (Social Butterfly) and actually completing that aspiration. After completing that entirely different aspiration I then switched back to the mind and body one. Moments there after I tried finishing the last task and it worked!
9) definitely try these workarounds and see if they work but always make sure you dont save so you dont waste valuable time of your sims lifespans just for things not to work out, good luck!
