Hello Ruth,
Sorry for the late reply. I checked out your site and it seems like you addex a prefix for EasyBlog urls "postalumnos" The reason the logout isn't working is because somehow the prefix remains even when EasyBlog has redirected to Joomla User page. I'm afraid as you are using MijoSEF, you will need to refer to them regarding this issue about how they affix the prefix. Hope this helps.
Thanks!