It is triggered when an adapter instance is moved from one collector to another; a new assignment is created, but the old assignment is not deleted.
This is a known issue within VCF Operations 9.1.0.x. A fix will be delivered in the upcoming VCF Operations update.
To keep up the latest updates, subscribe to this article. Refer to Subscribe to a Broadcom knowledge article by article or product
Open a support ticket with Broadcom referencing this KB article 452629 in the description. Refer to Creating and managing Broadcom cases.
Subscribe to this knowledge article to get updates on this issue.