Having the same issue over here. Utilizing Fortigate 100f + Edgeswitch + Unifi Access Points.
Desktop computers, cameras, other IoT devices that do not move do not have the same issues.
Laptops that move from LAN to Wifi or from wifi to LAN docking stations have connection issues and often get blocked by the Fortigate. I've noticed that when a user connects a different laptop to a floating docking station they grab the same IP the last client had. Instantaneously getting blocked by the Fortigate as it see's a new MAC with the same IP address?
What Firmware are you running OP?