Both ssh and mosh use a ptty on the remote device, but this doesn't provide scrollback itself, just a fixed size window where you can see some previous commands. Scrollback is a property purely of the local terminal.
Though after doing some research, it seems mosh skips some intermediate states when large amounts of lines are printed, causing them not to be sent to the client. This would cause the observed behaviour of no scrollback in the local terminal.
Though after doing some research, it seems mosh skips some intermediate states when large amounts of lines are printed, causing them not to be sent to the client. This would cause the observed behaviour of no scrollback in the local terminal.