Invalid Domain

I get this error when I try to run my chatbot:

rasa.core.domain.InvalidDomain: Domain specification has changed. You MUST retrain the policy. Detected mismatch in domain specification. The following states have been - removed: prev_utter_other_software - added: prev_utter_install_other_software sys:1: RuntimeWarning: coroutine ‘BaseEventLoop.create_server’ was never awaited

After training there are no errors, already checked the domain.yml file with yamllint and it checks ok, I only changed the name of a utterance in the domains file, because it was a mismatch with the action triggered template.

Train Policy? What does that mean?