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!