A 60 kg man stands on a spring scale in the lift. At some instant he finds, scale reading has changed from 60 kg to 50 kg for a while and then comes back to the original mark. What should we conclude.

For upward acceleration apparent Weight $=\mathrm{m}(\mathrm{g}+\mathrm{a})$
If lift suddenly stops during upward motion then apparent weight  $=\mathrm{m}(\mathrm{g}-\mathrm{a})$ because instead of acceleration, we will consider retardation.
In the problem it is given that scale reading initially was 60 kg and due to sudden jerk reading decreasing and finally comes back to the original mark i.e., 60 kg. So, we can conclude that lift was moving upward with constant speed and suddenly stops.