(EDIT: I've taken a look into this. From my end, everything seems good. Must be a freak bug. If you want to give me more information about it feel free to reply here, otherwise thank you for testing the game out!)
Hey there, thanks for playing! Basically The only way to regain sanity is to fully contain anomalies (build all modules) OR hire therapists. You need to make sure Therapists are researched, build a medical wing, build offices in the wing then you should be able to have a passive sanity raise!