There is a change related to limiting the use of port 443 in validations which was announced in January of last year and formally scheduled in October of last year.
In order to prepare for this change, Certbot's default behavior was changed in releases starting last month:
It's something of an oversimplification to say "port 80 was not used before", but it's true that there's been a recent change which has meant that Certbot users who were validating over port 443 have been switched to validating over port 80. We've been trying to accelerate this process because in the near future the Let's Encrypt certificate authority will disable TLS-SNI-01 validations entirely, as described in several of the posts I linked to.