Why is the connection with the Docker container lost?

Question

DigitalOcean

Ran into a strange issue with a DigitalOcean droplet with CoreOS and a Docker container.
Access to the site disappears, but after I log in via SSH to the droplet, access to the site appears.
This happens irregularly, on both droplets located in different regions.
- The first droplet with CoreOS inside which the nginx + php container.
- The first droplet with CoreOS inside which there are 2 nginx and nodejs containers. (nginx as a proxy to nodejs)