Version 1.50.2 introduces security mitigations by proposing new options for SSH.

2 of the 3 options have been introduced by SSH version 7.6:

• ssh(1): expand the StrictHostKeyChecking option with two new
  settings. The first "accept-new" will automatically accept
  hitherto-unseen keys but will refuse connections for changed or
  invalid hostkeys. This is a safer subset of the current behaviour
  of StrictHostKeyChecking=no. The second setting "off", is a synonym
  for the current behaviour of StrictHostKeyChecking=no: accept new
  host keys, and continue connection for hosts with incorrect
  hostkeys. A future release will change the meaning of
  StrictHostKeyChecking=no to the behaviour of "accept-new". bz#2400

Although it was released almost 3 years ago, this seriously breaks compatibility with non-recent Jenkins installations.

For instance, the current default Docker image for Jenkins is currently based off Debian Stretch which provides SSH 7.4 and doesn't support these new options:

$ docker run --rm -ti jenkins/jenkins:2.235 ssh -o StrictHostKeyChecking=off
command-line line 0: unsupported option "off".
$ docker run --rm -ti jenkins/jenkins:2.235 ssh -o StrictHostKeyChecking=accept-new
command-line line 0: unsupported option "accept-new".
$ docker run --rm -ti jenkins/jenkins:lts ssh -o StrictHostKeyChecking=accept-new
command-line line 0: unsupported option "accept-new".