The community permissions have been set that only users who are registered are able to post content.
A user recently posted content, however, it listed that the last modification was made by Guest.
This should not be possible. In addition, the community is only visible to users who are logged in.... so no idea why this happened. Due to the fact that it is an external community, I need to know if this is a known issue or how to prevent this from happening in the future.
Do you have Webservices enabled?
Web Services are disabled.