SonarQube is not involved in producing coverage reports, only in reading them. I would suggest you check to see if the annotation is actually having an effect on the JaCoCo report being produced (before it ever reaches SonarQube)
Yes it is a jacoco issue. This is discussed in stackoverflow and in jacoco mailing list.
get() method is excluded. But compiler internally created a method for lambda which is shown in red in the class level report. This seems to be a limitation of the jacoco @Generated annotation.