What is a cipher and where is it located?
In order for your local SSH client or other automated services to work, they need to use secure ciphers - encryption algorithms for securing information. Each Acquia instance contains a list of accepted ciphers, which are configured in the sshd_config file. Your local SSH client uses its own separate list of ciphers; these are generally also found in the sshd_config, located in /etc/ssh. Windows users may need to consult documentation specific to their software.
For your SSH client to connect to your Acquia instance, or for an automated service that depends on ciphers to function, at least one cipher in your SSH client or automated service's connection must match one of the ciphers in your Acquia instance. If your instance cycles through its ciphers and fails to find a correlating match in your SSH client or service, the connection will fail.