According to AWS's instance retirement plan about the Amazon Lightsail Instances, they can be stopped and started again after the retirement.
But, after their restart, these remaining CPU burst capacity is reset even though it was full before their retirement. I think it is reasonable that AWS returns these last capacity because instances are stopped for retirement by AWS, not user. resulted metric graph
But, AWS instance maintenance does not reset it. I just want like this.
I cannot address the request for burst capacity, but a stop/start of an instance is required to move the instance to new hardware and that is likely why it was reset.
@Rodney Lester, Thanks for your comment. My point is that the instance having full capacity is stopped by AWS's retirement, not me(or user). So I think AWS should return the instance with full capacity or last capacity amount if not full when it is started.