Ok so it turns out the the relief pressure was t set correctly. It was set to bypass at around 200 but was supposed to reach 305. It was prolly stalling at night when the cleaners were loading up their carts or whatever. You have to put your detective hat on when diagnosing these problems I have come to realize. Anyway, the elevator is coming up to speed nicely and after some adjusting all the floor levels and approaches are perfect. This was something we hadn't considered given the elevator had passed inspection and was sealed. Just proves that you can't assume things and take things for granted I suppose. We haven't had the elevator running for long but I am confident this was the issue with it.