RDS Serverless DB Auto-Scale Fail

I would recommend you to open a support case to troubleshoot the issue since you are getting an Internal Error.

In addition to that, please note that for scaling operations Aurora Serverless v1 first tries to identify a scaling point, a moment when no queries are being processed. Aurora Serverless might not be able to find a scaling point for the following reasons:

• Long-running queries
• In-progress transactions
• Temporary tables or table locks

In addition to the above, the "Minimum capacity", "Pre-warming" and "Scale-blocking operations" sections of this Best practices for working with Amazon Aurora Serverless blog post are probably helpful.