From Retraction Watch:
More than 70% of the citations in one journal were to other papers in that journal. Another published a single paper that cited nearly 200 other articles in the journal.
Now, Clarivate, the company behind the Impact Factor, is taking steps to fight such behavior, suppressing 33 journals from their indexing service and subjecting 15 more to expressions of concern — all for apparent self-citation that boosted the journals’ rankings.
The list includes some of publishing’s biggest players: Nine journals published by Elsevier, seven by Springer Nature, six by Taylor & Francis, and five by Wiley.