After upgrading Git Client plugin to version 3.2.1, Jenkins is unable to authenticate on Git (full stack trace in attachment):

com.trilead.ssh2.IOWarningException: Unsupported key format found 'ssh-rsa' while expecting rsa-sha2-256
  at com.trilead.ssh2.signature.RSAKeyAlgorithm.decodePublicKey(RSAKeyAlgorithm.java:111)

According to pom-file, git-client plugin 3.2.1 depends on trilead-ssh2 version build-217-jenkins-11. Checking trilead-ssh2 sources on the tag trilead-ssh2-build-217-jenkins-11, we see the mismatch with line number:

https://github.com/jenkinsci/trilead-ssh2/blob/ab0f2c88a402bf5b49748c96405467bfbcf03e76/src/com/trilead/ssh2/signature/RSAKeyAlgorithm.java#L102

Actually the exception is thrown in line 102, not 111. It seems that git-client plugin was built with a wrong branch of trilead-ssh2, that caused the regression.