Reports showing no results "Number of Distinct Clients"

Hi, I have problem with FortiManager reports. FortiManager (v5.2) is to connect 10 FG60D (v5.2), but one FG60D wifi report does not show "Number of Distinct Clients" (all other information show), on the other FortiGate shows Distinct Clients. I tried delete a Fortigate from the FortiManager and again to add, but did not help.

What could be wrong?