Jenkins will not continue pipeline after updating via Mercurial plugin
It looks like you have omitted to specify a branch in your scm checkout. Are you using the default branch in HG?
This Jenlins issue and the source code show that if you are not using the deault branch, you'll likely not see your changes pulled down even if the references are there.
If you are trying to build a non default branch give this a try
checkout changelog: true, poll: true, scm: [$class: 'MercurialSCM', branches: [[name: '*/yourbranch']], credentialsId: 'xxx', installation: 'TortoiseHg', source: 'C:\\Path\\to\\repo']