Yes it sounds like the magnet(s) have lost thier energy. You can easily recharge them with some rare earth magnets. It takes a good size one to do it though.

I am having a difficult time seeing where the magnet is in that picture. Is it a bar magnet? If so it would be best to unmount it to recharge it. The poles would go across the wide axis. One side is most likely painted white. That would be the south pole.

If you are leaning your guitar against amps or speaker cabs, this will slowly de-energize your magnets. Also riding on subways with you guitar. There are DC motors under the cars that are very powerful and emit a strong magnetic field.