This is a common problem with a number of causes.
The mechanism is driven by a motor with a rubber band link to the door mech. The rubber could be stretched or hard. Replace with new.
The drive strings could be greasy or frayed. Replace with new. Not an easy job!
The slider channels could be contaminated with sticky accumulation of dust and domestic greasy residues. Clean with Isopropanol on cotton wool bud and lubricate sparingly with silicone spray applied with cotton bud.
Could be all of the above!!!