502 dunglas/mercure error intermittently. How to understand why?

Question

symfony

For SSE I use the dunglas/mercure library. And periodically it throws out a 502 error. As I understand it, the client who got the error is disconnected from the ends. And how to understand what it lacks. There is enough memory on the server. The server is not loaded. What could be wrong?

no live upstreams while connecting to upstream, client: ...
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connect() to [::1]:1337 failed (101: Network is unreachable) while connecting to upstream, client:

Runs through supervisors in one instance.

Answer 1

For NGINX, localhost and 127.0.0.1 are actually different things. It periodically hammers on IPv6. If to register IP works normally.