What this Log Means?

For: HAProxy Load Balancer

Meaning: This error happens whenever the client is trying to establish a HTTPS connection and the client cyphers do not match with the ones accepted by the server. It often happens with old browsers if you have strict HTTPS requirements.

What to do: Monitor those error messages and if they are happening more often, you may need to loose your SSL/TLS settings to support old(er) browsers.