Time Slip is working on Sakura feelings confirmed, was having thought how it works when she slipped when he was with Umeko.
Sakura couldn't tell Makoto he was just a friend all along, due her being timid. What a mind fuck for Makoto it was...
Umeko was probably stalking them on Bali and taking advantage of commotion during Sakura Time Slip, snuck into bathroom and did the switchoroo.
When Sakura short Time Slip, it was really her, not Makoto hallucinations.
Sakura parents died in a car crash, her mom pulled her out before fire burst out, covering her before dying. No wonder she is so timid.
In conclusion, around yandare, never relax...