Before they headed up to the fort, an irate Rae had finished checking her catch and returned to her space to have a nap before evening descended, and she went on guard to make sure that nobody else was going to steal from her.
She had been active all day, so Karl didn't begrudge her the rest. Thor was returning to his space as well, since he couldn't climb to the fort, and Hawk had already settled into the nest he made in the fort last night.
That might be the reason that nothing came up. It would have smelled like Hawk and humans to them, and that would be enough to repel most forms of common monsters.
Even in her sleep, Karl could sense Rae's annoyance. The thief was most likely just some common grade monster who saw an opportunity and took it, but she took it very personally. In her space, there were no threats, and things stayed where she put them, so when someone looted her webs in the real world, she was not mentally prepared.