Make sure you wait long enough before pausing the game. There are two times when people pause that cause issues:

To fix this, make sure you are essentially standing on top of the bones - get as close to them as you possibly can before activating freecam and clicking on them. This means, if you aren't close enough to the bones to claim them when you have the freecam cheat activated, this cheat won't work. When the freecam cheat is activated, your creature can't move. Below are some common issues that might help you if the bones aren't respawning for you, or if you aren't able to claim them.