May 2021
@DonroaAkashuFound the spa, "Wakabamori spa" made by "maysbat". The stairs wasnt the problem here but the sauna. Seems that when rotating a lot, the game creates dead spots that prevents buidling.
May 2021
Reinstall fixed that problem. Not sure how many others it created...
June 2021
I'm having the same problem in Mt. Komorebi on PS4. 🙄