Comment # 10 on bug 1172898 from Lukas Ocilka

The error looks like coming from here:
https://github.com/yast/yast-yast2/blob/master/library/systemd/src/lib/yast2/systemd/target.rb#L52

The line contains:
undef_method :start, :stop, :enable, :disable, :restart

The error is:
failed with 'undefined method `start'

So ... "undefining" something that was not defined?
Connected with Ruby 2.7?