Fortimanager 7.4.3 device discover success but not showing on managed device or unauthorized device

Hi all. My college asking to me their FMG 7.4.3 have an issue. when device discover or adding manual serial number, task even said successful without any problem. but when he check on managed device, there is no shown any device that he add before. when trying add again, it said "device with serial number xxx already exist".

also, when I check with my college, I notice there is no "unauthorized device" menu on device manager.

I already check on release note but there is no mention about this. I notice on 7.4.0 there is an issue with FOS 7.0.12 but solving (i guess) on 7.4.3 (only mention issue with 7.2.9). And I check on compability matrix, 7.4.x still support to 7.0.x version. Is this new bug or something?

also when I check on FortiGate fabric connection, it said "connect" and "managed by fortimanager" but the IP/FQDN are blank.

there is no issue when testing on fmg 7.2.5.

here is the complete detail

FGT40F with 7.0.12

FGT60F with 7.0.14

FMG-VM64 with 7.4.3