The other day I faced this problem - server was not automatically renewing Let's Encrypt certificate:
produced an unexpected error: Problem binding to port 443: Could not bind to IPv4 or IPv6.. Skipping.
It took me some time to debug and find a solution, which is as easy as shutting down nginx server and then renewing lets encrypt (Solution found here: Trying to renew cert on nginx but getting “Problem binding to port 443: Could not bind to IPv4 or IPv6”)
sudo /etc/init.d/nginx stop
then
sudo certbot renew
and finally
sudo /etc/init.d/nginx start
Hope it helps!