In FortiOS 6.4.0, VLANs on a FortiLink interface configured to use a hardware switch may fail to come up upon upgrade or reboot due to an incorrect registration of the IP address of the switch VLAN interface.
The issue affects the FG-60E, FG-61E, FG-80E, FG-81E, FG-90E, and FG-91E models that contain a hardware switch and have FortiLink configured on it by default. Aggregate, physical, and software switch interfaces are not affected.
A workaround (not reboot persistent) is to re-configure the IP address on each VLAN interface to a different IP address. You may use an IP address in the same subnet and then change it back to the original IP address if desired.