MySQL returning only 1 row, multiple entries in the database
Your select statement includes group_concat().  This is an aggregation function.  Because there is no group by, this means that all the rows are treated as one group, and hence one row is returned.

Perhaps you mean:

SELECT publicationsId, title, summary, image, publicationDate, citation, dateAdded,
       GROUP_CONCAT(DISTINCT tagName) AS tagName,
       GROUP_CONCAT(DISTINCT publicationType) AS publicationType,
       employee_employeeId
FROM publications
LEFT JOIN publications_have_publicationTags ON publications_have_publicationTags.publications_publicationsId = publications.publicationsId
LEFT JOIN publicationTags ON publications_have_publicationTags.publicationTags_publicationTagId = publicationTags.publicationTagId
LEFT JOIN publications_have_publicationTypes ON publications.publicationsId = publications_have_publicationTypes.publications_publicationsId
LEFT JOIN publicationTypes ON publications_have_publicationTypes.publicationTypes_publicationTypeId = publicationTypes.publicationTypeId
LEFT JOIN employee_has_publications ON publications.publicationsId = employee_has_publications.publications_publicationsId
GROUP BY publicationsId, title, summary, image, publicationDate, citation, dateAdded, emplyee_employeeid
ORDER BY dateAdded DESC;