V brakes? If the return spring in the brake isn't broken.. dirt in the cable housing perhaps?
test.. take the cable off the brake ,

just like mending a puncture, and removing the wheel
[except for the wheel doesn't have to come out].

and see what pulling the cable directly feels like.

feel the caliper motion too, there may be a need to take the brake off the frame
and clean and re-grease the bushing /boss it rotates around.

then do the same to the other brake It's likely about due