Well I have great news, I have the same or very similar situation.
I got the dreaded Action Required email earlier this month, with the relevant line " vectorjohn.com (173.230.158.112) on 2018-12-14". I received it on 2019-01-28.
Since that time, I have not touched certbot in any way. No updates. Also:
root@localhost:/var/log/letsencrypt# certbot --version
certbot 0.21.1
Which according to other forum posts, is the old version that uses the soon deprecated tls-sni. I kept the old one because the instructions here say that I should expect errors if I run sudo certbot renew --dry-run. I get no errors at all. I verified I can get errors by setting the challenge explicitly to the deprecated one:
sudo certbot renew --dry-run --preferred-challenges tls-sni-01
But without doing that, the renew completes without issue.
Anyway, long story short, I am wary that anything I do actually fixes the potential problem since I can’t even reproduce it now with the old version. That, and my system (Ubuntu 17.10) says 0.21 is the newest so I can’t even update it.
For what it’s worth, I’m also on Linode, which is either a clue or a red herring.
Edit: One more thing. grep tls-sni /etc/letsencrypt/renewal/* finds nothing. I have not configured anything in there.
One more detail if it helps, I have three domains on the same system using letsencrypt. I only got the email about one of them.