Experts and BHG readers answer.
Sago palm not growing.
First, make sure it is truly not diseased. Check for scale - which appears to be a white powder but is really a tiny insect. Also look for brown, crusty bumps or lumps. Also could be scale. Ask for a control for your area at a local garden center.
Also, is the slow-growing one in the same light conditions as the other one? Sagos need bright light to grow well.
It may just be growing very slowly. Palms do this sometimes.