Based on support case with AWS, CloudWatch Events invoking Lambda should also specify the `source_arn`
Example, the resulting policy needs to be like:
```
{
"Condition": {
"ArnLike": {
"AWS:SourceArn": "arn:aws:events:us-east-1:0123456789:rule/my-cloudwatch-events-rule"
}
},
"Action": "lambda:InvokeFunction",
"Resource": "arn:aws:lambda:us-east-1:0123456789:function:my-lambda-function",
"Effect": "Allow",
"Principal": {
"Service": "events.amazonaws.com"
},
"Sid": "AllowMyCloudWatchEventRuleToCallMyLambda"
}
```
Steve Jansen