Generally the close assist has an actuator that is mounted to round bar just above the lock assembly. The closing of the latch (lock) activates the pull-in feature. Sometimes the actuator rotates on the bar so that the latch closing does not activate the electric switch to engage the pull in. This can be manually adjusted to resolve.

The path of least resistance though to try first is to spray WD40 or some other lubricant into the latch assembly with the hatch open and then just work the latch back and forth several times, spaying more lube into the assembly. Just work the latch by hand and use the release button to release and repeat. If that works you'll hear the pull-in motor engage. If not then proceed to the advise in the first paragraph.

Hope that helps

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)