DIAGNOSIS The lower blade guard gets jammed with sawdust, wood chips, or even a bit of melted plastic from cutting laminates. It's a physical obstruction, not a spring failure.
FIX Unplug the battery. Manually retract the guard by lifting the lever/ear on the side. Look inside the guard housing around the pivot points and where the guard meets the shoe. Use a stiff brush and compressed air to blast out all the debris. Work the guard back and forth manually. A drop of light oil on the pivot pin can help if it's sticky from sap.
IF THAT DIDN'T WORK Inspect the guard for physical damage. Is it bent? Is a piece of the shoe bent and blocking it? A bent guard or shoe requires part replacement for safety. Also, the return spring could be disconnected or broken, which is a less common but possible issue.
HEADS UP Never operate the saw with a stuck or manually tied-back guard. That's asking for a serious injury. If you can't free it up safely, it's time for professional repair.