java.lang.UnsupportedClassVersionError: com/trilead/ssh2/ServerHostKeyVerifier has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
at org.apache.tools.ant.AntClassLoader.defineClassFromData(AntClassLoader.java:1172)
at org.apache.tools.ant.AntClassLoader.getClassFromStream(AntClassLoader.java:1340)
at org.apache.tools.ant.AntClassLoader.findClassInComponents(AntClassLoader.java:1392)
at org.apache.tools.ant.AntClassLoader.findClass(AntClassLoader.java:1357)
at jenkins.ClassLoaderReflectionToolkit.loadClass(ClassLoaderReflectionToolkit.java:148)
at hudson.ClassicPluginStrategy$DependencyClassLoader.findClass(ClassicPluginStrategy.java:650)
at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
at org.apache.tools.ant.AntClassLoader.findBaseClass(AntClassLoader.java:1421)
at org.apache.tools.ant.AntClassLoader.loadClass(AntClassLoader.java:1108)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
at org.apache.tools.ant.AntClassLoader.defineClassFromData(AntClassLoader.java:1172)
at org.apache.tools.ant.AntClassLoader.getClassFromStream(AntClassLoader.java:1340)
at org.apache.tools.ant.AntClassLoader.findClassInComponents(AntClassLoader.java:1392)
at org.apache.tools.ant.AntClassLoader.findClass(AntClassLoader.java:1357)
at org.apache.tools.ant.AntClassLoader.loadClass(AntClassLoader.java:1112)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
at org.jenkinsci.plugins.gitclient.verifier.KnownHostsFileVerificationStrategy.getVerifier(KnownHostsFileVerificationStrategy.java:17)
at org.jenkinsci.plugins.gitclient.verifier.KnownHostsFileVerificationStrategy.getVerifier(KnownHostsFileVerificationStrategy.java:8)
at org.jenkinsci.plugins.gitclient.Git.getClient(Git.java:137)
at hudson.plugins.git.GitSCM.createClient(GitSCM.java:916)
at hudson.plugins.git.GitSCM.createClient(GitSCM.java:847)
at hudson.plugins.git.GitSCM.checkout(GitSCM.java:1297)
at org.jenkinsci.plugins.workflow.steps.scm.SCMStep.checkout(SCMStep.java:129)
at org.jenkinsci.plugins.workflow.cps.CpsScmFlowDefinition.create(CpsScmFlowDefinition.java:159)
at org.jenkinsci.plugins.workflow.cps.CpsScmFlowDefinition.create(CpsScmFlowDefinition.java:70)
at org.jenkinsci.plugins.workflow.job.WorkflowRun.run(WorkflowRun.java:311)
at hudson.model.ResourceController.execute(ResourceController.java:101)
at hudson.model.Executor.run(Executor.java:442)

Downgrading to v1.67 fixed the issue.