The chuck might have debris in the jaws, which could make adjusting the chuck harder or stiff.
Open the chuck fully and clean out any build-up of dirt and dust - preferably with compressed air.
This can be done by blowing compressed air (either from a can of compressed air or an air compressor) into the open chuck around the internal jaws until build up is removed.
You can also use a small cylindrical brush to clean the debris.