Upgrade automatically triggers an SQL rebuild post upgrade to 6.0, which must complete for FortiAnalyzer to function normally. Verify the database rebuild status using the following CLI command:
diagnose sql status rebuild-db
FortiAnalyzer's database rebuild is performed using Archive logs. Analytic logs will not be restored if FortiAnalyzer Archive logs are trimmed before performing a device database rebuild, therefore, it is important to review your storage data policy before upgrading and performing a database rebuild.
See the FortiAnalyzer Administration Guide for more information on Analytic vs Archive logs.