Diagnosis
Dirt, sand, or lack of lubrication in the folding latch assembly. The mechanism is exposed and grit can jam the internal spring and pin.
How to Fix It
Do not force it. Apply a penetrating lubricant (like WD-40 Specialist Dry Lube) directly into the latch mechanism. Work the release lever back and forth repeatedly until it frees up. Wipe away excess grime.
IF THAT DIDN’T WORK Inspect the safety locking pin on the opposite side of the stem. Sometimes this secondary pin gets misaligned. Push the stem slightly side-to-side while pressing the release lever.
Heads Up
Regularly clean and lightly lubricate the folding mechanism every few months, especially if you ride in wet or dusty conditions. A seized latch is almost always preventable.