Nothing new there—the only relevant aspect of the configuration in Jenkins is that you are using the known-hosts option. The question (if anyone cares) is why getPreferredServerHostkeyAlgorithmOrder failed. UnknownHostException trying to look up the slave? More likely, no known-hosts entry for that machine in recommendHostkeyAlgorithms, or multiple entries with different key types. Again I will leave it to mc1arke to evaluate what the desirable behavior is—I am just releasing a hotfix.
At any rate, try updating to 1.20 when it becomes available on the update center, which should be soon.