While attempting to create a Let’s Encrypt SSL certificate using certbot for a number of domains, I ran into something that appeared to be a timeout issue in the certbot client and/or one of the Python libraries used by it.
I found this thread, which recommends changing the MTU to 1300, and it does work. So, maybe this will help you too 🙂
In other words:
ifconfig eth0 mtu 1300
may help you out.