EC2 instance suddenly unreachable by SSH

For some reason, my EC2 instance, running Ubuntu, has suddenly become unreachable through my usual SSH instruction, although I have changed nothing. By running the ssh connection instruction with verbosity, i can read in the response: include /etc/ssh/ssh_config.d/*.conf matched no files Can it happen that the ssh configuration on the EC2 instance changes for some reason, without any action on my part?? Thank you very much for your help.