Today it's on the left side elevating and tomorrow it is descending. That is how escalators work in Singapore malls. Initially, I would get into trouble especially when I was inattentive. Several times, nearly meet with accident going the wrong side of the escalator.
Now, the reason for such changes could be strategic rather than random. By alternating the direction, the management of the mall will be able to regulate human traffic flow through the shops in the mall. Hence, no shop will be at a "dead end" with less traffic.