Can you describe what exactly you've tried? Serial and SSH not working on the same board seems very unlikely and implies there is no bootloader on it. Have you done anything with the board other than unbox and power it on (i.e. software/bootloader updates, or is this your OOB experience)?
If you can see the ttyusb address of the Ci40 in ubuntu you should be able to connect with any standard serial program using 115200. What exactly did you try, and do you see in this case? docs link.
If you leave the board powered on for about 1 minute then connect it via ethernet to your AP, do you see it get an IP (either on the router dhcp table, or via another machine connected to the same network)? If it does get an IP, can you SSH to it?
Apologies if you've tried all this, I don't know how to provide more assistance without more information about what you've done.