Unknown error in Lambda

Hello.

Does the same error occur even if you access from another browser or another PC?
Also, are there any policies set for the IAM user used to operate Lambda?
You can check whether the IAM policy is sufficient from the CloudTrail event history.
https://docs.aws.amazon.com/awscloudtrail/latest/userguide/view-cloudtrail-events.html

If the above does not resolve the issue, there may be a problem on the AWS side, so I recommend that you open a case with AWS Support under "Account and billing".
Inquiries under "Account and billing" can be made free of charge.
https://docs.aws.amazon.com/awssupport/latest/user/case-management.html