I guess you are using the [Me] filter to get your created by filter to work. And that’s OK if you’re using external user who have an account in your authentication provider such as Active Directory (AD). Then the simple solution would be like this:
But I guess that’s not the case here. I guess you have invited users through sharing you’re site to external users without giving them an account in your AD. What happens then is that you’re phasing two different patterns of user accounts.
Your internal users follow the pattern
domain\user, which SharePoint can resolve as a user and filter by. Your external users have a different user ID pattern which SharePoint can’t resolve and as a consequence can’t filter. When the filter fails, the result is that all documents are shown instead of only those for the external user.
In SharePoint Online/Office 365 the pattern for external user is
<external e-mail address>#EXT#@<www.your-company.com> which differs from
domain\user in SharePoint.