I'm having the same bug.
After a while of playing (about 2 hours in, to be more precise), my spear stops working. Selecting it shows me holding a plain stick, and clicking the shark does nothing. This has happened in 2 different games. Second time, I assumed this meant it was broken (I don't even know if tools CAN break), so I tossed it into the ocean and made a new one. No difference.