not sure if your jeep has either the torsion rods or the gas filled lift rods (otherwise known as gas charged struts!) OR BOTH. if these are wearing out, or not helping to close the glass could be a contributing factor.
if it has the torsion rods above the glass make sure they are still in their keeper holes and slots. (be careful as they are under tension) the torsion rods are not on the glass, but usually on the door.
it appears your lift gate glass is just ‘helped’ by the gas charged strut lifters. these go for about 20.00 each. and take about 20 minutes to swap out. i don’t know which sockets you need, or just a torx, but when that happens it is an easy fix.
and the gas lift rods are easily replaceable too if needed.