I think I've figured out the reason the Owlbear Cub sometimes doesn't show up at the Goblin Camp. If you fight the mother, you have to make sure she doesn't enrage (she'll scream "What have you done?!"). It's caused by the cub being attacked, which may happen even if you don't directly attack the cub. For example, when the mother leaps around, the AoE would count as an offensive action against the cub (even tho you didn't atk it directly). I was able to get the Owlbear Cub to leave the cave (after 1 long rest) by killing the mother in 1 turn. Cheers!
Did not work. Killed the mom in 1 turn, long rested, several times and the cub did not show up at Goblin Camp and just keeps on munching on her corpse.
