A zipper that separates behind the zipper slider is a very common zipper failure mode, esp. on tents, backpacks and luggage. It's an easy fix with
How to Repair a Broken Slider on a Suitcase Zipper - iFixit Repair
Jean Zipper Repair - iFixit Repair Guide
Patagonia Zipper - iFixit
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Fix Your Broken Zipper Problems
5 Ways to Fix a Broken Zipper - wikiHow
Repair Café Malmö - Trouble with a zipper? Often it's an easy fix
How to Fix a Zipper
Jean Zipper Repair - iFixit Repair Guide
Quick-Fix: Replacing a Zipper Pull - iFixit Repair Guide