This worked in 2.5, looks new in 2.6?
timeout(time: 1, unit: 'HOURS') {
dataset = input([message: 'Select thing', parameters: [[$class: 'ChoiceParameterDefinition', choices: thingArrayString, description: 'Select thing', name: 'thing']]])
}
 
with 2.6 proceed fails with:
Caused by: java.lang.NoSuchMethodError: org.jenkinsci.plugins.workflow.support.steps.input.InputStepExecution.proceed(Ljava/lang/Object;)Lorg/kohsuke/stapler/HttpResponse;
at io.jenkins.blueocean.rest.impl.pipeline.PipelineStepImpl.submitInputStep(PipelineStepImpl.java:200)
at java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:627)