I did used the "Lansweeper device tester" to verify the SNMP connection.
The connection wasn't working so I did the needed change in the fortiswitch a while ago. The switch is visible in Lansweeper, i can see witch port is down or up. But I still doesn't have the mac adress and I cannot know wich assets are connected where 😞
I've contacted support and they seem's clueless :S
I don't have any Fortinets, but have you tried the SNMP tester? I do that quickly on stuff I have issues with to see if it says 'SNMP Disabled or Wrong Community'