After deleting NSX Edges from vCenter, the user credentials for the Edges are not removed from the SDDC Manager.
The "root" and "admin" accounts for the target edges may show as disconnected.
VCF 9.0
This is caused by a failed password rotation / remediation process within SDDC. In the SDDC Password Management pane you will find a failed task for the target node:
Cancel the failed password task from SDDC. After the nightly sync that runs for VCF 9, the users should be removed automatically.