High CPU Utilization on Redshift Leader Node Despite No Active Queries.

Hello AWS Community,

I'm experiencing an issue with my Amazon Redshift cluster where the leader node is consistently showing 99-100% CPU utilization, while the compute nodes remain below 30%. This issue has persisted for over 8 hours and began around the time of an automatic cluster restart during a maintenance window at 3:30 AM. Despite pausing all external data ingestion and manually restarting the cluster, the high CPU usage continues with no active user queries running.

Here are the details of my environment and what I have checked so far:

1. Redshift cluster with 1 leader node and 2 compute nodes, operational for the past 2 years.
2. No running queries or loads according to the Redshift console.
3. All external data ingestion is paused.
4. Manually restarted the cluster post the maintenance window; however, the CPU issue persists.
5. Additionally, I noticed some long-running VACUUM operations that seem to be taking longer than usual for each table. Here's what I have attempted to diagnose and resolve the issue: Checked system tables for any background processes or errors, but found nothing that should lead to such high CPU usage.
6. Reviewed logs for any abnormalities around the time the CPU spike began.
7. Attempted to optimize VACUUM operations and evaluated locks and session activity.

Despite these efforts, I'm unable to pinpoint the cause of the high CPU usage on the leader node. I'm looking for insights or suggestions on further steps I can take to diagnose and resolve this issue. Any help or guidance from this community would be greatly appreciated! Thank you!