The mosh protocol is specifically designed such that reordering won't happen (since it does use UDP as a base protocol, it requires this protection). I think they'd be very interested to hear about any such bugs you have regarding that.
Also, as far as I was aware, ssh provided no scrollback either. Any such scrollback is a property of the (local) terminal you're using, not ssh itself.
> Any such scrollback is a property of the (local) terminal you're using, not ssh itself.
The Mosh client is also a terminal emulator (similar to screen); part of the reason it can be so efficient is that it isn't just another layer in the network stack over which standard lines of text travel, it is a remote console viewer (like VNC is for graphical desktops, only sending parts of the desktop that have changed; and if there is a massive wall of text spamming the screen, it will just show you the end result rather than sending it all)
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.
Also, as far as I was aware, ssh provided no scrollback either. Any such scrollback is a property of the (local) terminal you're using, not ssh itself.