Cloudwatch logs - some log groups can not be saved properly

Hi there,
We’ve just upgraded to Grafana7.0.1 and we are excited about the new feature - cloudwatch logs.
But we face an issue that, after we create a Cloudwatch panel, next time when we edit it again, the previous log group we selected is missing, we have to select again. This seems only happen to those log groups’ names without ‘/’. For example, if the log group is called ‘MySerice’ then we face this issue but if the name of the log group is ‘/aws/apigateway’, then it’s fine. I am guessing maybe the ‘/’ does the magic!
Could anyone please help?