private static final String SONAR_ISSUES_BASE_URL = "/api/issues/search?ps=1&projectKeys=";

I don't believe this URL is getting what you expect.  It returns the total number of issues in the entire sonarqube system whether you have the projectKeys request parameter or not.

I believe to get the issues by project you need the following:
$sonarurl="${SonarHostUrl}api/measures/component?metricKeys=code_smells,ncloc,duplicated_lines_density,open_issues,sqale_rating,critical_violations,blocker_violations,major_violations,vulnerabilities,complexity,sqale_index,sqale_debt_ratio,violations&component=$SonarProjectKey"
 
You have to specify the metrics you want returned
 
Then on the returned JSON, you need to get:

$sonmeasures=$sonresult.component.measures
This object will contain the metrics only for the project you are looking for.
 
I'd be happy to talk further if anything isn't clear.  I love this plugin, btw.  Makes our grafana dashboards very helpful.