This might be due to mismatching settings on the Fortigate and FSSO collector.
Can you please: 1. Make a screenshot of the fsso connector settings on the Fortigate 2. On the Collector Agent (CA) open the Fortinet Single Sign On Agent Configuration console and click the "Set Directory Access Information" button.
If the directory access mode is "Standard", then the User Group source on the FSSO connector has to be configured as "Collector Agent"
if the directory access mode is "Advanced" , then the User Group source on FSSO connector has to be configured as "Local"
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