alt Hacker NewsAccording to https://www.youtube.com/watch?v=tZ8ehplVFp4&t=636 the handrail is driven by a friction wheel that wears out over time, so its diameter gradually decreases and the handrail speed slows down (until it gets too out of sync, and the friction wheel is replaced).
So when it’s new it feels broken, the friction wheel wears until it works properly for a period of time, and then it feels broken again, so they replace the wheel with on that goes back to making it still feel broken and start the cycle again. How frustrating.