Hi Volunteer 19. If the lift works correctly after reset by switching off the power and switching it on, most probably it has nothing to do with the hydraulic system, but is related to the door system.
Has the technician disabled relevelling?
1. Maybe after standing all night the piston is sinking and the lift is slipping past the door zone sensor. And if this happens, the door won't open when a call is registered at the first floor. But technically it should answer other floor calls. Have you checked calling the lift from the upper floors when this happens?
2. Or maybe after some time period the door circuit is timing off and is not coming on when a call is registered.

I think it is point 1, and when power is switched off and on, the lift travels to the floor to reset its count and reenters the doorzone again to make the doors operate.Since you say that the lift works fine the whole day, I suspect it is a sinking/relevelling disabled problem.

If this is the case let us know and we can suggest corrective action.