Fortiswitch with fortilink across HP5406

Gave up on the idea of private vlans since they have not worked even with support calls.

Changed to this configuration.

Fortigate 500E into HP5406 chassis switch, Fortilink enabled. Fortiswitch 248D connected to chassis port C9

Untagged vlan 1.   Fortiswitch get's ip.

Tagged vlan 17 (internal users).  Set port 2 to native vlan17. Laptop get's ip.

248D shows connected to fortigate under managed switch.

Stays online for 30 seconds then drops off. Give it 30-45 seconds, it's back online.

Anything to check to see why it may be doing this?