Well I would say there are a few things that you should check :
Check diagnostic settings
- Review the diagnostic settings configured for your Load Balancer and ensure that the Log Analytics Workspace is selected and the appropriate logs are enabled.
- Confirm that the correct table is specified for storing the logs.
Validate permissions:
- Check the permissions for the workspace and verify that the account has the "Contributor" or "Log Analytics Contributor" role assigned.
Check log ingestion status:
- Use a query like the following to verify if logs are being received:
Heartbeat
| where TimeGenerated > ago(1d)
| summarize Count() by bin(TimeGenerated, 1h), SourceSystem
Validate log retention:
- If the retention period is too short, it might result in logs being automatically deleted before you can view them
Please accept as answer if this helps.