I just had a look at the help pages and there isn't much there but they've got some problems that they're fixing. If you're using Android they say:
Hi Wattpadders,
Just to let you know, we are aware of story updates not appearing for stories in your library. We are trying to work on a fix as we speak, but there is a workaround for the time being:
Please delete the story from your library, wait a minute, and then add it again to your library will let you see the newest update to the story.
We're very sorry for the inconvenience of this all, and we thank you for your patience!
The Wattpad Team
Not sure if that will fix it or not, but have a go and if it still doesn't work I'll get onto them with an email.
Hope this helps!