Rubber tree stagnating?

Hello,

A few months ago, I picked up a fairly large rubber tree from a house clearance. It's in a pot that also has a watering aid. I keep it in a spot where it's not directly exposed to sunlight, but it's not dark either.

When I first got it, it grew a new leaf, but now it's essentially stagnant—it's still alive, but it's not growing any further. Is this normal? If not, what might it need?