Device hostname not showing in Fortigate logs

[adli01]

I cannot see the device hostname within Fortigate logs when they communicate internally, meaning within LAN but when the devices access the Internet meaning from LAN to WAN, i can see the hostname just fine

Device detection is already turned on for the LAN interface
Is there anything else I should look for?

[srajeswaran]

Is the LAN to LAN communication cross Fortigate or the routing/switching happens without fortigate involvment? Can you share the sample log without hostname?