Garage door trolley no longer attached
I fixed this issue by calling our neighbor, who realized that the trolley was too loose and the left lip was a bit curved. We flattened the lip (with a hammer) and then squeezed it along the other axis (v-shaped cut) using a vice. We then slipped the trolley back on and it worked without any issues.
Note: When squeezing the trolley to get a tighter v-shape, the metal is rather springy. You need to tighten the vice quite a bit to get it to deform the right amount.