Build failure

hudson.remoting.ProxyException: net.sf.json.JSONException: Invalid JSON String
at net.sf.json.JSONSerializer.toJSON(JSONSerializer.java:143)
at net.sf.json.JSONSerializer.toJSON(JSONSerializer.java:103)
at net.sf.json.JSONSerializer.toJSON(JSONSerializer.java:84)
at hudson.plugins.sonar.client.WsClient.getCETask(WsClient.java:53)
at org.sonarsource.scanner.jenkins.pipeline.WaitForQualityGateStep$Execution.checkTaskCompleted(WaitForQualityGateStep.java:240)
at org.sonarsource.scanner.jenkins.pipeline.WaitForQualityGateStep$Execution.start(WaitForQualityGateStep.java:176)
at org.jenkinsci.plugins.workflow.cps.DSL.invokeStep(DSL.java:322)
at org.jenkinsci.plugins.workflow.cps.DSL.invokeMethod(DSL.java:196)
at org.jenkinsci.plugins.workflow.cps.CpsScript.invokeMethod(CpsScript.java:124)
at jdk.internal.reflect.GeneratedMethodAccessor373.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1225)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1034)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:41)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:180)
at org.kohsuke.groovy.sandbox.GroovyInterceptor.onMethodCall(GroovyInterceptor.java:23)
at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onMethodCall(SandboxInterceptor.java:163)
at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:178)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:182)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:152)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:152)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:152)
at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.methodCall(SandboxInvoker.java:17)

Start with hudson.plugins.sonar.client.WsClient.getCETask at WsClient.java:53 and the surrounding WaitForQualityGateStep stack trace. Determine why the response is rejected as an invalid JSON string, then verify that the affected build completes successfully without this exception.