I am not that familiar with the cabling systems even though I've owned a couple popups.
I would think you could have gotten slack on that corner cable and maybe it just came off a pulley.
I would look underneath or start pulling some panels to see if I could get access to the cable system
There are some youtube videos on how to repair popup cable systems. Maybe that will shed some light on your issue.
Keep us posted on your fix.
2016 Toyota Tundra SR5, 5.7 V8