Fortinac-F Multiple Host Problem

I have this problem with Fortinac. I have a port and computer A is plugged into this port. When computer B is plugged into the same port, both computer A and B appear under the port even though computer A is not plugged in. Even though I deleted computer A, it is still under the port. The device is quarantined because there is more than one device. Fortiswitch can be used.