Unable to use SSL web access - error SSL_ERROR_NO_CYPHER_OVERLAP

I’ve migrated my main router from a hex lite to a hex, and copies the configuration. Everything seems to be working, except for SSL access being refused with SSL_ERROR_NO_CYPHER_OVERLAP - “Cannot communicate securely with peer: no common encryption algorithm(s)”.

So far as I can tell, there is a valid SSL certificate installed. The software is the latest stable version.

What could cause this?

It seems to have corrected itself. No idea why.