The run-condition plugin claims to support xtrigger causes, but doesn't check the correct class. An XTrigger cause always has the org.jenkinsci.lib.xtrigger.XTriggerCause class even if the installed plugin creates a custom cause class.

I have a proposed solution in a github pull request:
https://github.com/jenkinsci/run-condition-plugin/pull/9

In order to get the right cause, I had to add a dependency on the xtrigger-lib.